The present disclosure relates to a communication technique for convergence of a 5G communication system for supporting a higher data transmission rate beyond a 4G system with an IoT technology, and a system therefor. The present disclosure may be applied to an intelligent service (for example, smart home, smart building, smart city, smart car or connected car, health care, digital education, retail business, security and safety-related service, etc.) based on a 5G communication technology and an IoT-related technology. The present invention provides a method for processing a packet by a terminal, the method comprising the steps of: receiving configuration information for packet processing from a base station; determining a count value for processing a packet to be transmitted to the base station, based on the configuration information; and processing the packet based on the determined count value, wherein the length of the count value is the same as the length of a packet data convergence protocol sequence number (PDCP SN) of the terminal.