A negotiation processing method for a security algorithm, a control network element, and a control system where the negotiation processing method for a security algorithm includes selecting, by a control network element according to a security capability of first user equipment (UE) and a security capability of second UE, a security algorithm supported by both the first UE and the second UE, and notifying, by the control network element, the selected security algorithm to the first UE and the second UE, and hence, negotiation of a security algorithm between two UEs in proximity communication can be implemented under the control of a control network element.