The present invention discloses a friend addition method, device and system, a client and a server. The method comprises the steps that: a first client sends an external contact addition legality verification request to a first server based on an external contact service module, wherein the request comprises a first user identifier of a first user corresponding to the first client and a second user identifier required being added corresponding to the second user, and the first user and the second user are users in different groups; the first server performs external contact addition legality verification; if the verification passes, a verification pass message is sent to the first client; the first client sends the external contact addition request to the first server based on the externalcontact service module; and the first server sends a friend addition request to the second client based on the external contact service module of the second client corresponding to the second user identifier, and an agreement response message sent by the second client terminal responding to an agreement friend addition command of the second user is received, and the friend addition success massage is sent to the first client.