In order to enhance the detection performance of array radar under mainlobe interference,this paper proposes a method of radar anti-mainlobe interference based on fractional domain filtering,which can effectively suppress the mainlobe interferences.The proposed method searches for the mainlobe interference in the fractional domain by using fractional Fourier transform,determines the position of interference based on its peak values.The interference is then filtered in the fractional domain,and the echo signal is further processed by a blocking matrix to better eliminate the mainlobe interference.Simulation experiments validate the effectiveness of the proposed algorithm.