An embodiment of the invention discloses a method, a terminal and a system for joining a social group. The method for joining the social group includes: registering a first mobile terminal of a social network to obtain the state of motion of the first mobile terminal, establishing communication connection with a second mobile terminal which registers the social group in a certain range according to the state of motion, and sending through the established communication connection a request for joining the social group to the second mobile terminal that registers the social group; and the second mobile terminal that registers the social group sending group joining information to a social group server according to the request for joining the social group, and thus the social group server enabling a social network user that registers the first mobile terminal to join the social group according the group joining information. By adoption of the method for joining the social group, immediate and quick social group joining can be realized, so that the user can realize effective communication in a social group product conveniently.