In the paper, we propose a new blind symbol rate estimation of weak signal with fixed sampling rate based on cyclic spectrum and wavelet transform. Firstly, the FFT characteristics is used to estimate the carrier frequency and the received signal is moved to the baseband by Digital Down Converter (DDC). Then, the wavelet transform is used for pre-estimating the symbol rate. Thirdly, the symbol rate estimation is proposed on the basis of cyclostationary theory and pre-estimated symbol rate. Simulation results verified the correctness of this method with MPSK signal. When the Signal to Noise Ratio (SNR) is −10 db, the approach proposed in this paper can accurately estimate the varied symbol rate with fixed sampling rate.