A method and apparatus for preventing loss of uplink data in wireless communication system is provided. A central unit (CU) of an integrated access and backhaul (IAB)-donor receives, from a wireless device, uplink data through a source IAB-node. The CU of the IAB-donor receives, from the source IAB-node, a message which informs that uplink packets among the uplink data are remained on the source IAB-node, wherein the message is related to handover procedures of the wireless device from the source IAB-node to a target IAB-node. The CU of the IAB-donor proceeds the handover procedures, after receiving the uplink packets.