Provided are a method and an apparatus for supporting security of user traffic when a central unit (CU)-control plane (CP) and a CU-user plane (UP) of a gNB are separated in a wireless communication system. According to an embodiment of the present invention, the CU-CP of the gNB selects an encryption algorithm, generates a user plane security key for the CU-UP on the basis of the encryption algorithm, and transmits the user plane security key for the CU-UP to the CU-CP. The CU-UP applies the received user plane security key. The CU-CP is a logical node constituting the gNB that hosts a radio resource control (RRC) and a packet data convergence protocol (PDCP)-C protocol, and the CU-UP is a logical node constituting the gNB that hosts a PDCP-U protocol.