i am banned from server but can i make a new steam and buy gta again and will i be able to join back ?
No you can’t. It based on a multitude of factors.
But ban evasion is not something we deal with on this forum.
Go to the servers forum and appeal the ban, if they accept it you’ll get another chance, don’t screw up again.
If they reject it, consider not doing it on future servers.