A control signaling processing method, a device, and a system relate to the field of communications technologies, to perform integrity protection on control signaling exchanged between a DU and UE in a CU-DU separated access network architecture. The method includes: determining, by a DU, integrity protection parameters and an integrity protection algorithm, where the integrity protection parameters and the integrity protection algorithm are used to perform integrity protection on a signaling radio bearer between the DU and UE; determining, by the DU, a message authentication code MAC-I based on the integrity protection parameters and the integrity protection algorithm; and receiving, by the DU, control signaling sent by an RRC layer of the DU, and sending, to the UE, the control signaling carrying the MAC-I.