Abstract: An improved algorithm based on cross Wigner-Ville distribution,which is derived for the special case where the frequency is zero in Wigner-Ville distribution (WVD) of time-frequency analysis is used to detect LFM signal, in this case the WVD includes all the information of original signals, such as frequency and phase. This method is efficient for reducing noise, for single LFM signal or small target embedded in some large targets they can be detected in low SNR by the algorithm. The simulation results prove its effectivity.