A method for performing data transmission by a user equipment (UE) in a wireless communication system is disclosed. The method comprises steps of receiving a message indicating a change of a Radio resource control (RRC) state from a RRC CONNECTED state to a RRC INACTIVE state, wherein the message includes information related to a configured grant (CG) and a threshold; if a time gap between a current time and an uplink grant occasion associated with the configured grant is larger than or equal to the threshold, triggering a random access (RA) procedure for the data transmission; and performing the data transmission based on the RA procedure in the RRC INACTIVE state, wherein, if the time gap is smaller than the threshold, the data transmission is performed based on the uplink grant occasion associated with the configured grant.