An HARQ-ACK feedback method, a terminal and a network side device are provided. The method includes: when a HARQ-ACK of a PDSCH is required to be transmitted on a PUSCH scheduled by uplink DCI in a multiplexing mode, if the uplink DCI includes a DAI, determining an HARQ-ACK feedback codebook transmitted on the PUSCH, based on at least one of a judgement result of whether the PDSCH scheduled before the uplink DCI is required to transmit the HARQ-ACK on the PUSCH in a multiplexing mode or the DAI, and a maximum quantity of PDSCHs capable of being transmitted after the uplink DCI.