The present invention discloses a method and device for a terminal to transmit data under an RRC connected state. The method includes the step that: after a terminal in an RRC connected state is switched to a target cell or receives a PDCCH command, when the terminal initiates non-competition random access, a base station sends a timing advance command corresponding to the terminal to the terminalwhen sending downlink data or signaling corresponding to the terminal. With the method and the device disclosed by the present invention adopted, the problem of the delay and additional signaling overhead of downlink data or signaling transmission caused by random access after a terminal is switched to a target cell or receives a PDCCH command in the prior art can be solved.