An Instant Messaging (IM) method and server are provided. The method includes: receiving instance login information sent by an IM client, wherein the instance login information at least includes login information of a user of the IM client and instance information of a terminal located by the IM client (101); authenticating identity of the user of the IM client, according to the login information in the instance login information (102); when the authenticating is passed, allocating an instance number for the IM client, according to the instance information in the instance login information, wherein the instance number is configured to uniquely identify the IM client (103). The server includes a receiving module (801), an authenticating module (802) and an allocating module (803). By adopting the method and server provided, multipoint login of one login account may be effectively achieved, and multiple aspects requirements of a user may be satisfied.