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. The present invention provides a method of a base station for supporting an inter-system handover from an evolved packet system (EPS) system to a 5th generation (5G) system. The present application provides a method for transmitting HARQ-ACK information, including steps of: detecting, by a UE, a PDCCH and receiving a PDSCH scheduled by the PDCCH; for one slot of one carrier, determining, according to a configured slot pattern and a configured PDCCH monitoring occasion, the HARQ-ACK occasion and the number of HARQ-ACK bits occupied by the one slot; and, generating, by the UE, an HARQ-ACK codebook according to the HARQ-ACK occasion and the number of HARQ-ACK bits occupied by the one slot, and transmitting HARQ-ACK information. By the method of the present invention, the number of HARQ-ACK bits to be fed back within each slot is reduced, and the feedback overhead is reduced; moreover, the number of bits of the generated HARQ-ACK codebook changes semi-statically, so that the confusion between a base station and a UE is avoided.