The invention relates to a space diversity method for physical layer network coding in a communication system, and belongs to the technical field of wireless communication. The method comprises the following steps of: arranging a plurality of distributed relay station antennas between two single antenna users, sending data to a relay station by a user, estimating channel information between the relay station and a user antenna by the relay station, acquiring a channel matrix, selecting a binary phase shift keying modulation mode by the user, sending interactive information among the users to the relay station, performing combined detection on the received superposed signals by the relay station to acquire network coding symbols, selecting an antenna set, performing space-time coding on the network coding symbols, then sending the coded network coding symbols to the user, performing space-time decoding on the space-time coded symbols by the user, and decoding the estimation values of the network coding symbols according to the interactive information to acquire data information of an opposite user. The method improves the frequency spectrum utilization rate and energy utilization efficiency of a bidirectional relay network and remarkably improves the bidirectional communication reliability of the users.