when searching kevin mccarthy, it instantly write within the URL:
http://www.web.com/search/kevin+mccarthy

however when I change http://www.web.com/search/kevin+mccarthy with http://www.web.com/search/kevin-mccarthy, no result made an appearance.

I've attempted modify in wp-includes/rewrite.php but have no idea things to replace

Why would you like to replace the + having a -? I'm not sure Wordpress well, however it appears like it's while using part after /search/ because the Peaceful same as a question string and thus is most likely unencoding it in the same manner. Whenever a + seems inside a query string, it translates to some space, so the search could be for "kevin mccarthy" &mdash but when you alter it to some -, the search is going to be for "kevin-mccarthy" which appears enjoy it most likely is not what you would like... More about the particular URL encoding utilized in query strings on this Wikipedia page.