In an ISS process, the initiator sends a first SSW frame in different sector directions by sequentially using an antenna in m antennas, where m is not less than 1 and is less than or equal to N, and in an RSS process, the initiator receives a second SSW frame in a parallel (e.g., simultaneous) omnidirectional manner by using M antennas, where the second SSW frame is sent by a responder in different sector directions, each second SSW frame carries information used to indicate a first SSW frame with best quality in the ISS process, and the M antennas include at least the m antennas, and determines an optimal transmit beam in the ISS process based on the received second SSW frame.