The present invention provides a communications system, a base station, a user equipment, and a signaling transmission method. The system includes: a first base station and a second base station. User data transmission exists between the first base station and a UE; the first base station performs control signaling interaction with the UE by using a first signaling radio bearer; and the second base station performs control signaling interaction with the UE by using an SRB0, an SRB1, or an SRB2, where the first signaling radio bearer is different from the SRB0, the SRB1, and the SRB2. The technical solutions of the present invention can solve a problem of configuring a radio resource of an air interface connection between an enhancement-layer base station and a UE.