Abstract: It is difficult for a passive radar to detect weak targets under the background of strong jamming coming from large targets,near air fleet or deception jam.Based on the connection between strong and reference signals,the relationship between the amplitude-range-Doppler surface and the ambiguity function of the reference signal was deduced,and a detection method for weak targets was proposed based on two-dimension FIR(finite impulse response) system identification.Simulation results indicate that the proposed method can restrain the strong signal beyond 60 dB,and even to weak targets with an echo SNR(signal to noise ratio) of-24 dB,they can be detected.