We are going to create a user and the same we want to configure the same as replication agent in author instead of admi user which comes with built in AEM/CQ.Here my doublt is do we need to have the same user gets created in publisher instance also.Please help if any one has any idea on this.
I assume that you asking about how config replication to use a different users for transport. You can specify any username and password you wish on the Transport tab of the replication agent config. The are some limitations you need to keep in mind however:
The user much exist on your target publish server - your transport user is not a user on your author server - it is a user on you publish server.
The user must have full read/write/create/delete permissions on any content you want it to replicate. So for example if you don't grant it access to the /apps directory then replication on anything in the /apps directory will fail.
It probably needs read and edit ACL permissions too in order for permissions to get replicated but I am not 100% certain of that.