Embodiments of the present application relate to a method and apparatus for hybrid automatic repeat request-acknowledge (HARQ-ACK) feedback for carrier aggregation (CA). A method according an embodiment of the present application may include receiving at least one downlink transmission; generating a first HARQ-ACK sub-codebook for the at least one downlink transmission; determining whether to generate a second HARQ-ACK sub-codebook; and transmitting a HARQ-ACK codebook. The HARQ-ACK HARQ-ACK codebook includes the first HARQ-ACK sub-codebook in response to the second HARQ-ACK sub-codebook determined not to be generated, or includes the first HARQ-ACK sub-codebook and the second HARQ-ACK sub-codebook in response to the second HARQ-ACK sub-codebook determined to be generated. The present application avoids misunderstanding between a base unit and a remote unit when generating the HARQ-ACK feedback for CA.