Abstract: A blind method for symbol rate estimation of MPSK/MQAM signals by using the nonlinear process is presented. Utilizing the phase changing between inter-symbols and through the nonlinear transforming of zero IF signals, the spectral lines corresponding to the symbol rate can be extracted. The fourth-order cumulant is used for suppressing the strong background noise of symbol rate spectral lines in this paper. This method is robust to Gaussian noise and can achieve good estimation results with lower SNR. At the same time, it has lower computational complexity and is applicable to different shaping filters and different modulation orders of MPSK/MQAM signals.