Abstract: The multipath effect of low altitude target seriously affects the detection performance of radar and multipath detection is the key link of low angle tracking. In this paper, the multiple monopulse ratio model of low altitude target under multipath effect is established. The multiple monopulse ratio is used to indicate the interference intensity of mirror reflection. According to whether multipath exists or not, the statistical characteristics of the complex monopulse ratio are analyzed and the decision threshold is derived to form the multipath existence decision algorithm of low altitude target. The relationship between algorithm performance and target altitude, distance and signal to noise ratio (SNR) is analyzed by simulation. Simulation results show that the proposed algorithm is still effective under low SNR conditions. In plane flying and landing scenarios, the existence of multipath can be accurately determined, which provides support for improving the performance of radar measurement.