A method and a user equipment for HARQ process ID selection are provided. The method includes: receiving a configuration message to configure a Configured Grant (CG) configuration and a set of HARQ process IDs that is available for the CG configuration, the set of HARQ process IDs including a first HARQ process ID for retransmission and a second HARQ process ID for initial transmission; determining that a CG physical uplink shared channel (PUSCH) corresponding to the CG configuration becomes available for transmission; selecting, based on a first HARQ process ID selection procedure, the first HARQ process ID or the second HARQ process ID from the set of HARQ process IDs for the CG PUSCH; and transmitting, based on the selected first or second HARQ process ID, a first Medium Access Control (MAC) Protocol Data Unit (PDU) for retransmission or a second MAC PDU for initial transmission on the CG PUSCH.