Disclose are: a communication technique for merging, with IoT technology, a 5G communication system for supporting a data transmission rate higher than that of a 4G system; and a system therefor. The present disclosure can be applied to an intelligent service (for example, smart home, smart building, smart city, smart car or connected car, health care, digital education, retail, security and safety-related services, and the like) on the basis of a 5G communication technology and an IoT-related technology. One embodiment of the present invention relates to a method and a device for accelerating data processing of a double connection in a next generation mobile communication system.