how to prevent spam

If your site appears in google or any other search engine than spammers will start to submit fake comments on your site.

You may install anti-spam plugin.

It blocks spam in comments automatically and without captcha.

but i set ” No new register” but they still able to register new account and keep submit spam comment …
that my main concern.

There is no “one size fits all” method that will protect your comments; spammers use many tactics. Consider using multiple defenses. Remember spammers change the way they attack so you must keep your choices updated.

Combating Comment Spam

but i set ” No new register” but they still able to register new account and keep submit spam comment

This is some kind of magic ??

yah this is scarry magic trick ….

sonny – are you using Akismet? That’s the best first step for dealing with spam.

https://codex.www.ads-software.com/Akismet

yes i’m using akismet …. and will try more captcha or questionnaire plugin soon …..

just wondering how they register when my registration is disable …. ??

Yes, that’s a good question – you might want to make sure your site has not been hacked:

https://sitecheck.sucuri.net/scanner/