The towed radar active decoy (TRAD) flies with the airplane to form the triangular state through the maneuver flight, and the geometry relationship among the radar, airplane and decoy changes rapidly. In the course of jamming, the Doppler frequency characteristics of the airplane and the decoy are both time varying. Traditional FFT is unavailable to display the variety of frequency along with the time, brings out the expanded spectrum and declined resolution, and that causes the method based on the expanded spectrum limited when used for jamming detection. Based on the analysis of the jamming and time frequency characteristics, the LFM model of the target echo and jamming signal are approximated for sections, the time-frequency analysis is used to exhibit the variety law of the Doppler frequency vs time, and the Wigner-Ville Distribution and Hough transform are combined and adopted to detect the peak value of the multiple signals. The threshold is designed according to the decoy features, and the detection of presence of TRAD is realized. Simulation results under terminal condition illustrate the performance of the method.