I have stored plain text password in config file. Is there any way blur or replace password with XXXXX.

when I open config file in vim I want to see

password = XXXXX

The easiest and most secure way of obscuring the password in the config file is

DON'T PUT A PLAINTEXT PASSWORD IN A FILE

Any solution otherwise using vim for what you describe will only obscure the password for you. Other people can open/read the file without vim, seeing the password.

If, for some reason, this is the use case you want (say, for projecting a presentation, and you are for some ungodly reason using a password that the audience could use to exploit something live (Why the hell are you doing that), you can write an autocmd that will obscure everything after the equals sign.

autocmd BufRead * silent! %s/=[^=]*$/=XXXX/

But, note that this is only for a presentation: the text is actually rewritten and you would not want to save this file.

Your other choice would be using 7.3's syntax highlighting to mark the text as concealed.