The invention discloses a method for realizing asynchronous transmission in a parallel QR decomposition relay satellite forwarding system. The implementation steps are as follows: Firstly, a least square formula is utilized to obtain a channel matrix of each user; A scientific satellite signal frame structure and a relay satellite signal frame structure are determined by using a frame format thathead and tail signals are zero; and the ground station enables the received signals to form a receiving signal matrix, exchanges positions to obtain an equivalent channel matrix, utilizes orthogonal decomposition to obtain a receiving signal unitary matrix and an upper triangular equivalent matrix, and finally utilizes an upper triangular matrix judgment formula to obtain decoded relay satellite signals. According to the method, the existing modulation mode and spatial complexity are not changed, the problem that the dimension of a constructed matrix is large is solved, and the reliability ofcommunication in a relay satellite downlink communication system is improved.