A method and apparatus for performing contention resolution for contention based physical uplink shared channel (CB-PUSCH) transmission in a wireless communication system is provided. A user equipment (UE) performs a first hybrid automatic repeat request (HARQ) transmission on a CB-PUSCH to a network, and determines whether contention on the CB-PUSCH is resolved. The CB-PUSCH is a channel for UL data allocated by a pre-configured UL grant which is shared by multiple UEs. If a UL grant includes an identity of the UE, it is determined that contention on the CB-PUSCH is resolved. The UE may perform a second HARQ transmission for the first HARQ transmission on a PUSCH to the network by using the UL grant.
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