The invention discloses a method for establishing groups across instant messaging systems. The method comprises the following steps: a group owner establishes a new instant messaging group, selects group members from a friend list to enter the group, and updates an own group list; the instant messaging system where the group owner is located creates the instant messaging group, generates group attribute information; the instant messaging system where the group owner is located sends the group attribute information to all instant messaging systems where the group members are located; the instant messaging systems where the group members are located maintain the group attribute information and forward the group attribute information to all group members; and all group members update own group lists according to the group attribute information. By adoption of the method for establishing groups provided by the invention, the users of different instant messaging systems can perform instantmessaging in the same group, thereby realizing the group instant messaging across instant messaging systems.