Aim at problems of detection and parameter estimation of poly-phase coded signals in low SNR, a method based on the expanded fractional Fourier transform(EFRFT) is proposed. According to the characteristics that poly-phase coded signals’ time frequency ridges are parallel, EFRFT improves the kernel function of the fractional Fourier transform(FRFT) and cumulates the energy of ridges. It can complete the signal detection and estimate signals’ modulation parameters. Simulation shows this method can effectively detect signal and exactly estimate parameters of signal in low SNR.