Considering the characteristic of Pulse Code Modulation-Frequency Modulation (PCM-FM) signal, a Fast Fourier Transform (FFT) based autocorrelation detection method is proposed. Firstly, this method can adapt to high dynamic situation by using autocorrelation processing to eliminate the influence of Doppler frequency change on detection performance.Then the detection performance of proposed method is improved under the condition of low SNR by FFT of autocorrelation output. The simulation result shows that high probability detection of PCM-FM signal at low SNR and high dynamic situation can be realized by the proposed method.