I want to use the root user to remotely login the Linux visa ssh, but access denied.
I can use another use named jany to sucessfully remotely login the Linux visa ssh, then I use "su root" command to sucessfully login.
why I couldn't login to the Linux with the root user like "jany" visa ssh.

expect to an answer.

thks!

You'll need to edit your /etc/ssh/sshd_config, find the line "PermitRootLogin no" and change to "PermitRootLogin yes"

For the benefit of the OP, this is also considered bad security practise.

It depends upon your exact setup but it is considered bad security practice to allow root login as if this is done on an internet connected computer it allows brute forcing of the root login. This can be mitigated by using passwordless login using encryption keys but it's still not a good idea to expose the root account.
As an example I have run SSH servers on virtual machines which I have exposed to the internet. Even though they were not left running long the logs were full of failed attempts to log in as root and, on one occasion where my password was set to "password", the attacher successfully logged in.