A method by which a first wireless device maintains beamforming in a wireless AV system, according to one embodiment of the present invention, comprises the steps of: transmitting a packet including a non-training field and a plurality of training fields to a second wireless device, wherein the non-training field is transmitted on the basis of the best sector combination from among a plurality of candidate sector combinations predetermined between the first wireless device and the second wireless device, and the plurality of training fields is transmitted on the basis of the plurality of candidate sector combinations; receiving candidate beam feedback information as a response to the plurality of training fields; determining, on the basis of the candidate beam feedback information, whether a channel change due to an obstacle occurs; and updating the best sector combination on the basis of the candidate beam feedback information when it is determined that the channel change occurs.