diff --git a/Makefile b/Makefile
index 9a8c6c79d72da9..e5111d4083e5be 100644
--- a/Makefile
+++ b/Makefile
@@ -967,6 +967,7 @@ LIB_OBJS += apply.o
 LIB_OBJS += archive-tar.o
 LIB_OBJS += archive-zip.o
 LIB_OBJS += archive.o
+LIB_OBJS += attach.o
 LIB_OBJS += attr.o
 LIB_OBJS += base85.o
 LIB_OBJS += bisect.o
diff --git a/attach.c b/attach.c
new file mode 100644
index 00000000000000..a3bdefd872af5c
--- /dev/null
+++ b/attach.c
@@ -0,0 +1,15 @@
+#include "git-compat-util.h"
+#include "environment.h"
+#include "attach.h"
+
+const char *default_attachments_ref(void)
+{
+        const char *attachments_ref = NULL;
+        if (!attachments_ref)
+                attachments_ref = getenv(GIT_ATTACHMENTS_REF_ENVIRONMENT);
+        if (!attachments_ref)
+                attachments_ref = attachments_ref_name;
+        if (!attachments_ref)
+                attachments_ref = GIT_ATTACHMENTS_DEFAULT_REF;
+        return attachments_ref;
+}
diff --git a/attach.h b/attach.h
new file mode 100644
index 00000000000000..12819f0db6f9cb
--- /dev/null
+++ b/attach.h
@@ -0,0 +1,15 @@
+#ifndef ATTACH_H
+#define ATTACH_H
+
+/*
+ * Return the default attachments ref.
+ *
+ * This the first of the following to be defined:
+ * 1. The '--ref' option to 'git attach', if given
+ * 2. The $GIT_ATTACHMENTS_REF environment variable, if set
+ * 3. The value of the core.attachmentsRef config variable, if set
+ * 4. GIT_NOTES_DEFAULT_REF (i.e. "refs/attachments/commits")
+ */
+const char *default_attachments_ref(void);
+
+#endif
diff --git a/builtin/attach.c b/builtin/attach.c
index 1a7dc23809c336..63a59f80e980a0 100644
--- a/builtin/attach.c
+++ b/builtin/attach.c
@@ -1,7 +1,187 @@
 #include "builtin.h"
 #include "gettext.h"
+#include "parse-options.h"
+#include "config.h"
+#include "pathspec.h"
+#include "setup.h"
+#include "object-store.h"
+#include "object-file.h"
+#include "object-name.h"
+#include "hex.h"
+#include "attach.h"
+#include "refs.h"
+#include "tree-walk.h"
+#include "tree.h"
+
+static const char * const git_attach_usage[] = {
+	N_("git attach add [--commitish] <file>"),
+	NULL
+};
+
+static const char *const git_attach_add_usage[] = { 
+	N_("git attach add [--commitish] <file>"),
+	NULL
+};
+
+static int write_attach_ref(const char *ref, struct object_id *attach_tree,
+			    const char *msg)
+{
+	const char *attachments_ref;
+	struct object_id commit_oid;
+	struct object_id parent_oid;
+	struct tree_desc desc;
+	struct name_entry entry;
+	struct tree *tree = NULL;
+	struct commit_list *parents = NULL;
+	struct strbuf buf = STRBUF_INIT;
+
+	if (!ref)
+		attachments_ref = default_attachments_ref();
+
+	if (!read_ref(attachments_ref, &parent_oid)) {
+		struct commit *parent = lookup_commit(the_repository, &parent_oid);
+		if (repo_parse_commit(the_repository, parent))
+			die("Failed to find/parse commit %s", attachments_ref);
+		commit_list_insert(parent, &parents);
+	}
+
+	tree = repo_get_commit_tree(the_repository,
+				    lookup_commit(the_repository, &parent_oid));
+	init_tree_desc(&desc, tree->buffer, tree->size);
+
+	while (tree_entry(&desc, &entry)) {
+		switch (object_type(entry.mode)) {
+		case OBJ_TREE:
+			fprintf(stderr, "entry.path: %s\n", entry.path);
+			continue;
+		default:
+			continue;
+		}
+	}
+
+	if (commit_tree(msg, strlen(msg), attach_tree, parents, &commit_oid,
+			NULL, NULL))
+		die(_("Failed to commit attachment tree to database"));
+
+	strbuf_addstr(&buf, msg);
+	update_ref(buf.buf, attachments_ref, &commit_oid, NULL, 0,
+		   UPDATE_REFS_DIE_ON_ERR);
+
+	strbuf_release(&buf);
+	return 0;
+}
+
+/*
+ *  * Returns 0 on success, -1 if no attachments, 1 on failure
+ */
+static int write_attach_tree(const struct pathspec *pathspec,
+			     struct object_id *attach_tree,
+			     struct object_id *attach_commit)
+{
+	struct strbuf file_buf = STRBUF_INIT;
+	struct strbuf attach_tree_buf = STRBUF_INIT;
+	struct dir_struct dir = DIR_INIT;
+	struct object_id oid;
+	struct stat st;
+	unsigned flags = HASH_FORMAT_CHECK | HASH_WRITE_OBJECT;
+
+	dir.flags |= DIR_SHOW_OTHER_DIRECTORIES | DIR_SHOW_IGNORED_TOO |
+		     DIR_KEEP_UNTRACKED_CONTENTS | DIR_HIDE_EMPTY_DIRECTORIES;
+	fill_directory(&dir, the_repository->index, pathspec);
+
+	// 有没有现成的API解决这个问题， 将dir转换为tree？
+	// 没找到，自己写吧
+	for (int i = 0; i < dir.nr; i++) {
+		strbuf_reset(&file_buf);
+
+		if (lstat(dir.entries[i]->name, &st))
+			die_errno(_("fail to stat file '%s'"),
+				  dir.entries[i]->name);
+
+		if (!(S_ISREG(st.st_mode))) {
+			warning(_("attachment is not a regular file, skipped '%s'"),
+				dir.entries[i]->name);
+			continue;
+		}
+
+		if (strbuf_read_file(&file_buf, dir.entries[i]->name, 0) < 0)
+			die(_("unable to read filepath '%s'"),
+			    dir.entries[i]->name);
+
+		if (write_object_file_flags(file_buf.buf, file_buf.len,
+					    OBJ_BLOB, &oid, flags))
+			die(_("unable to add blob from %s to database"),
+			    dir.entries[i]->name);
+
+		strbuf_addf(&attach_tree_buf, "%o %s%c", 0100644,
+			    dir.entries[i]->name, '\0');
+		strbuf_add(&attach_tree_buf, oid.hash, the_hash_algo->rawsz);
+	}
+
+	if (attach_tree_buf.len <= 0)
+		die(_("no attachments found in given pathspec"));
+	else
+		write_object_file(attach_tree_buf.buf, attach_tree_buf.len,
+				  OBJ_TREE, attach_tree);
+
+	strbuf_release(&file_buf);
+	strbuf_release(&attach_tree_buf);
+	return 0;
+}
+
+static int add(int argc, const char **argv, const char *prefix)
+{
+	struct pathspec pathspec;
+	struct object_id attach_tree;
+	struct object_id attach_commit;
+	char *attach_commitish = NULL;
+	char *attachments_msg = "Attachments updated by 'git attach add'";
+
+	struct option options[] = {
+		OPT_STRING(0, "commit", &attach_commitish, N_("commit"),
+			   N_("the commit which the attachments reference to")),
+		OPT_END()
+	};
+
+	parse_options(argc, argv, prefix, options, git_attach_add_usage,
+			     PARSE_OPT_KEEP_ARGV0);
+	attach_commitish = attach_commitish ? attach_commitish : "HEAD";
+
+	if (repo_get_oid_commit(the_repository, attach_commitish,
+				&attach_commit))
+		die(_("unable to find commit %s"), attach_commitish);
+
+	parse_pathspec(&pathspec, 0,
+		       PATHSPEC_PREFER_FULL | PATHSPEC_SYMLINK_LEADING_PATH,
+		       prefix, argv + 1);
+	if (!pathspec.nr)
+		die(_("nothing specified, nothing to attach"));
+
+	if (write_attach_tree(&pathspec, &attach_tree, &attach_commit))
+		die(_("unable to write attach tree object"));
+
+	if (write_attach_ref(NULL, &attach_tree, attachments_msg))
+		die(_("unable to write attach ref"));
+
+	clear_pathspec(&pathspec);
+	return 0;
+}
 
 int cmd_attach(int argc, const char **argv, const char *prefix)
 {
-	return error(_("subcommand `%s' not implement yet"), argv[0]);
+	parse_opt_subcommand_fn *fn = NULL;
+	struct option options[] = { OPT_SUBCOMMAND("add", &fn, add),
+				    OPT_END() };
+
+	git_config(git_default_config, NULL);
+
+	argc = parse_options(argc, argv, prefix, options, git_attach_usage,
+			     PARSE_OPT_SUBCOMMAND_OPTIONAL);
+
+	if (!fn) {
+		error(_("subcommand `%s' not implement yet"), argv[0]);
+		usage_with_options(git_attach_usage, options);
+	}
+
+	return !!fn(argc, argv, prefix);
 }
diff --git a/config.c b/config.c
index b330c7adb4a5ef..3ba9f57bfff0fb 100644
--- a/config.c
+++ b/config.c
@@ -1717,6 +1717,11 @@ static int git_default_branch_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.attachmentsref")) {
+		attachments_ref_name = xstrdup(value);
+		return 0;
+	}
+
 	/* Add other config variables here and to Documentation/config.txt. */
 	return 0;
 }
diff --git a/environment.c b/environment.c
index 9e37bf58c0c682..2c76145e0d17b7 100644
--- a/environment.c
+++ b/environment.c
@@ -73,6 +73,7 @@ enum push_default_type push_default = PUSH_DEFAULT_UNSPECIFIED;
 #endif
 enum object_creation_mode object_creation_mode = OBJECT_CREATION_MODE;
 char *notes_ref_name;
+char *attachments_ref_name;
 int grafts_keep_true_parents;
 int core_apply_sparse_checkout;
 int core_sparse_checkout_cone;
diff --git a/environment.h b/environment.h
index e5351c9dd95ea6..c8effe1d49b708 100644
--- a/environment.h
+++ b/environment.h
@@ -55,6 +55,8 @@ const char *getenv_safe(struct strvec *argv, const char *name);
 #define GIT_OPTIONAL_LOCKS_ENVIRONMENT "GIT_OPTIONAL_LOCKS"
 #define GIT_TEXT_DOMAIN_DIR_ENVIRONMENT "GIT_TEXTDOMAINDIR"
 #define GIT_ATTR_SOURCE_ENVIRONMENT "GIT_ATTR_SOURCE"
+#define GIT_ATTACHMENTS_REF_ENVIRONMENT "GIT_ATTACHMENTS_REF"
+#define GIT_ATTACHMENTS_DEFAULT_REF "refs/attachments/commits"
 
 /*
  * Environment variable used in handshaking the wire protocol.
@@ -190,6 +192,8 @@ enum object_creation_mode {
 	OBJECT_CREATION_USES_RENAMES = 1
 };
 
+extern char *attachments_ref_name;
+
 extern enum object_creation_mode object_creation_mode;
 
 extern char *notes_ref_name;
diff --git a/t/t6700-attach.sh b/t/t6700-attach.sh
new file mode 100755
index 00000000000000..9cb9b41646e18e
--- /dev/null
+++ b/t/t6700-attach.sh
@@ -0,0 +1,18 @@
+#!/bin/sh
+
+test_description='basic git attach test cases'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+       test_commit 1st
+'
+
+test_expect_success 'attach: add regular files' '
+       echo "content of foo" >foo &&
+       echo "conteng of bar" >bar &&
+       foo_blob=`cat foo | git hash-object --stdin` &&
+       bar_blob=`cat bar | git hash-object --stdin` &&
+       git attach add foo bar
+'
+test_done
\ No newline at end of file