原因

在版本3.0中文件名字是a.txt，在3.1版本将a.txt改为了b.txt，合并时3.0的a.txt找不到对应文件，导致合并失败；
此时intellij message标签页中提示，

Warning:Integration interrupted. There are unresolved conflicts or skipped items.

并且在subversion version control中提示

此时，intellij的local changes会提示 local deleted

解决

在合并前，不要修改文件名字。

svn官方文档的说明

关于改了文件名，就断了联系这一点，svn官方文档说是可以修复的，

Repairing File Renames
Sometimes your friendly IDE will rename files for you as part of a refactoring exercise, and of course it doesn’t tell Subversion. If you try to commit your changes, Subversion will see the old filename as missing and the new one as an unversioned file. You could just check the new filename to get it added in, but you would then lose the history tracing, as Subversion does not know the files are related.
A better way is to notify Subversion that this change is actually a rename, and you can do this within the Commit and Check for Modifications dialogs. Simply select both the old name (missing) and the new name (unversioned) and use Context Menu → Repair Move to pair the two files as a rename.

亲测试后得知，tortoise svn的rename功能 intellij已经实现了关联，但是只是在当前分支实现了关联，修改文件名字后，查看svn history可以看到以前的commit信息，但是如果从旧分支合并到新分支，还是合并不了，不能跨分支；

参考

https://tortoisesvn.net/docs/release/TortoiseSVN_en/tsvn-dug-rename.html