diff --git a/kernel/model/export_merge.go b/kernel/model/export_merge.go
new file mode 100644
index 000000000..8c182620c
--- /dev/null
+++ b/kernel/model/export_merge.go
@@ -0,0 +1,94 @@
+// SiYuan - Build Your Eternal Digital Garden
+// Copyright (c) 2020-present, b3log.org
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package model
+
+import (
+	"github.com/88250/lute/ast"
+	"github.com/88250/lute/parse"
+)
+
+func mergeSubDocs(rootTree *parse.Tree) (ret *parse.Tree, err error) {
+	ret = rootTree
+	rootBlock := &Block{Box: rootTree.Box, ID: rootTree.ID, Path: rootTree.Path}
+	if err = buildBlockChildren(rootBlock); nil != err {
+		return
+	}
+
+	for i := 0; i < 1024; i++ {
+		if err = walkBlock(ret, rootBlock); nil != err {
+			return
+		}
+
+		if nil == rootBlock.Children {
+			break
+		}
+	}
+	return
+}
+
+func walkBlock(tree *parse.Tree, block *Block) (err error) {
+	for _, c := range block.Children {
+		if err = walkBlock(tree, c); nil != err {
+			return
+		}
+	}
+
+	for i := len(block.Children) - 1; -1 < i; i-- {
+		c := block.Children[i]
+		nodes, loadErr := loadTreeNodes(c.Box, c.Path)
+		if nil != loadErr {
+			return
+		}
+
+		for j := len(nodes) - 1; -1 < j; j-- {
+			tree.Root.LastChild.InsertAfter(nodes[j])
+		}
+	}
+	block.Children = nil
+	return
+}
+
+func loadTreeNodes(box string, p string) (ret []*ast.Node, err error) {
+	tree, err := LoadTree(box, p)
+	if nil != err {
+		return
+	}
+
+	for c := tree.Root.FirstChild; nil != c; c = c.Next {
+		ret = append(ret, c)
+	}
+	return
+}
+
+func buildBlockChildren(block *Block) (err error) {
+	files, _, err := ListDocTree(block.Box, block.Path, Conf.FileTree.Sort)
+	if nil != err {
+		return
+	}
+
+	for _, f := range files {
+		childBlock := &Block{Box: block.Box, ID: f.ID, Path: f.Path}
+		block.Children = append(block.Children, childBlock)
+	}
+
+	for _, c := range block.Children {
+		if err = buildBlockChildren(c); nil != err {
+			return
+		}
+	}
+	return
+}