The present application relates to method and apparatus for downlink slot set determination. One embodiment of the present disclosure provides an apparatus comprising: a receiver that receives a first number of downlink transmissions indicating a first slot for transmitting corresponding HARQ-ACK feedback and receives a second number of downlink transmissions indicating a second slot for transmitting corresponding HARQ-ACK feedback; a processor that determines a first downlink slot set for the HARQ-ACK feedback transmitted in the first slot and a second downlink slot set for the HARQ-ACK feedback transmitted in the second slot, and determines the first downlink slot set and the second downlink slot set have at least one overlapped slot; and a transmitter that transmits a first HARQ-ACK codebook in the first slot for the first downlink slot set and a second HARQ-ACK codebook in the second slot for the second downlink slot set, wherein HARQ-ACK feedback for each of the at least one overlapped slot is included in either the first HARQ-ACK codebook or the second HARQ-ACK codebook.