Abstract: A method, device and system for selecting a security algorithm are provided. The method includes: a core network receives an attachment request initiated to a broadband cluster network by a first terminal (UE), wherein the attachment request carries first security capability information supported by the first UE; the core network determines a group to which the first UE belongs, and obtains security capability information of each second UE in the group; and the core network selects a security algorithm supported by both the security capability information of the first UE and the security capability information of each second UE; and sends the selected security algorithm to the first UE as a security algorithm of the group.