A method, a user equipment and a base station are provided. The method is for transmitting Hybrid Automatic Repeat Request-Acknowledgement (HARQ-ACK) information in a communication system in which two carriers are configured, which includes: a user equipment encodes a codeword of the two carriers. The codeword represents encoded HARQ-ACK information of a first carrier and a second carrier according to a specific encoding scheme of dual-carrier configured with Multiple-Input Multiple-Output (DC-MIMO). The user equipment then transmits the encoded codeword of the two carriers to a base station. Therefore, bit error ratio (BER) and detection error cost are decreased, power overhead is saved, and a cubic metric (CM) value of the system is not affected, thereby enhancing the performance of the system.