The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method for processing a packet by a transmission device in a wireless communication system according to an embodiment of the present invention comprises the steps of: checking whether a data radio bearer (DRB) mapped to a quality of service (QoS) flow changes from a first DRB to a second DRB; and when the DRB changes from the first DRB to the second DRB, transmitting, to a reception device, information on a last packet transmitted through the first DRB in the QoS flow.