A method for reporting Hybrid Automatic Repeat Request Acknowledgement (HARQ-ACK) is provided. The method is applicable to a time-division duplex (TDD) wireless communication system and includes the following steps: receiving downlink information from a base station with multiple serving cells, calculating a report number of each serving cell, which is a number of subframes of the corresponding serving cell whose acknowledgements have to be reported, and providing report information to the base station in an uplink subframe of a serving cell specified by the base station. The multiple serving cells use multiple uplink-downlink configurations. The report number of at least one of the serving cells is determined according to a downlink association set of the uplink subframe of the serving cell specified by the base station. The report information includes the acknowledgements that have to be reported by each of the serving cells.