Aimed at the problems that as the angle between the target and the jamming line of sight decreases, the anti-jamming performance of monopulse radar decreases noticeably, this paper proposes an improved anti-jamming method of monopulse radar based on distributed auxiliary antenna. Distributed auxiliary antennas are added in the radar system, the maximization of anti-interference improvement factors must be taken as a guideline, and integrated single-pulse radar beams and distributed auxiliary antenna beams are utilized for performing adaptive interference suppression in the beam domain. Finally, CFAR detection is used to verify the anti-interference performance of the proposed algorithm, in comparison with other methods. The numerical simulation results show that the proposed anti-jamming method can effectively improve the anti-jamming improvement factor and target detection probability, and has a good anti-jamming performance while the target and interference line of sight are at a small angle.