As a new radar jamming strategy, UAV cluster electronic countermeasures need to study its influence mechanism on radar detection. Based on the principle of radar detection, this paper has discussed the influence of drone cluster body, cluster suppression interference, cluster forwarding interference, cluster coherent interference on radar parameter measurement; and has analyzed influencing factors such as SNR, JSR, drone density, the amplitude ratio between target echo and UAV body echo. The body of UAV cluster has a poor interference effect on the radar. The main reason is that the body of UAV is small in size and the corresponding radar echo power is low. The three interference methods, suppression interference, forwarding interference and coherent interference, have good interference effects when used in cluster interference. Through the above analysis, the influence mechanism of UAV cluster on radar parameter measurement in electronic countermeasures is summarized.