The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) 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 by a terminal configured with a dual connectivity for processing data is provided. The method includes acquiring the data, determining a cell group to preprocess the data based on an amount of the data and a threshold value, preprocessing the data by the determined cell group before receiving an uplink grant for transmitting the data, and determining a radio link control (RLC) sequence number of the preprocessed data based on the uplink grant if the uplink grant is received.