This application provides a data processing method and device, to implement bearer mapping of control plane signaling of user equipment on each interface. An IAB system includes a centralized unit CU, a distributed unit DU, a first IAB node, and a second IAB node. The method includes: generating, by the CU, a downlink F1AP message, where a message included in the downlink F1AP message is one or a combination of the following: an F1AP message of a terminal device, an F1AP message of the first IAB node, and an RRC message of the second IAB node; and sending, by the CU, the downlink F1AP message to the DU, and indicating that a message type of the message included in the downlink F1AP message is one of the following: an RRC message type, an F1AP message type, or an RRC message type and an F1AP message type.