A method and apparatus supporting UP security for MO-EDT in CU-DU split in a wireless communication system. A central unit (CU) receives, from a distributed unit (DU), a first message including a PDCP Data PDU, wherein the PDCP Data PDU is configured by a wireless device. A CU calculates a HASHDATA from the PDCP Data PDU. A CU verifies a Short MAC-I of the wireless device based on the HASHDATA. A CU transmits, to the DU, a second message to setup a UE context for the wireless device in the DU based on the verification.