is it exact&fast&easy to convert between C++ and Blueprint?
as Git is not able to show the difference of Revisions of Blueprint change, so convert to C++ before commit is a good idea?
and when pull from git rep, convert from C++ to Blueprint?
or is there any way to sync Blueprint to its C++?
I don’t think what you want is possible. Unreal does have some limited git integration which might let you use the built-in visual blueprint diff tool. You can also use the tool manually but you need both copies of the blueprint available to compare.
is it able to show the difference between to revision of BP? what’s the tool? it’s not able to use the tool together with Git?
If you’ve got git source control enabled on your project (“source control” next to the save icon in the main editor toolbar) then you might be able to do File/Diff on your blueprint window. There’s also File/Merge which may or may not be useful to you.