how to block register / comment / and more security ?

Login as admin

By default registration is disabled
You can verify under Settings > General and then look for Membership

For comment go to Settings > Discussions and check under Default article settings

thanks

is it easy to another one hack admin password wordpress ?

Hacking a password would just involve guessing it – if a password is easy to guess then it is easy to hack.

about SQL Injection hack
is it possible ?

It’s fair to assume that the core of WordPress is secure. If you want ways of improving security on your site, read this article: https://codex.www.ads-software.com/Hardening_WordPress