The present invention relates to a method of transmitting uplink (UL) data by a user equipment (UE) in a wireless communication system. In particular, the method includes the steps of: based on the UE transmitting the UL data on a first UL resource of a configured grant (CG) con-figuration based on a Hybrid-ARQ (HARQ) process, starting a CG retransmission timer for the HARQ process and a CG timer for the HARQ process; based on a second UL resource of the CG configuration not being configured between an expiration time point of the CG retransmission timer and an expected expiration time point of the CG timer, stopping the CG timer upon expiration of the CG retransmission timer; and performing retransmission of the UL data based on the HARQ process after the expected expiration time point of the CG timer.