Abstract: In view of the problem that the existing radar signal detection method in the detection threshold is difficult to determine, this paper puts forward a method of adaptive detection and parameter estimation of LFMCW signal based on the periodic fractional Fourier transform(PFRFT). First, with the introduction of PFRFT, the matching characteristics and processing gain of PFRFT was analyzed; Then, the probability statistical properties of LFMCW signal in PFRFT domain was derived in the background of the Gaussian white noise, the detection threshold was determined adaptively by Neyman-Pearson criterion, and it implements the rapid detection and parameter estimation of LFMCW signal in low SNR. The analytical theory and simulation results show its effectivity.