Use pandoc to realize it.

• Install pandoc

sudo apt-get install pandoc

• Create or edit file ~/.gitconfig to add

[diff "pandoc"]
     textconv=pandoc --to=markdown
     prompt = false
[alias]
     wdiff = diff --word-diff=color --unified=1
 

• In git working directory, create or edit file .gitattributes

*.docx diff=pandoc

• Use git wdiff to show diff  between commits and working tree or between two commits  for .docx file, commitsId can get use command git log

git wdiff file.docx

git wdiff commitsId1 commitsId2 file.docs