Embodiments of the present invention relate to the field of communications technologies, and provide a feedback information sending method, a terminal device, and an access network device, so as to send feedback information on an unlicensed spectrum. According to the embodiments of the present invention, the terminal device receives, in a downlink subframe in a downlink subframe set, downlink data, and then determines, in at least one uplink burst, a sending subframe used for sending feedback information corresponding to the downlink data, where the downlink subframe set is a subset of a set consisting of a downlink subframe associated with the sending subframe, and each of the at least one uplink burst includes at least one uplink subframe; and then sends, in the sending subframe, the feedback information. The solutions provided in the embodiments of the present invention are used when the feedback information is sent.