It is important to estimate the Signal-to-Noise Ratio (SNR) of unknown emitter signal accurately. In order to resolve the disadvantages of present algorithm, a novel method is proposed in this letter. We extract and normalize the information of zero frequency of received signal by the Wigner-Vile Distribution (WVD) transformation and then get the approximate power of original signal by mathematic transformation, at last, we get the estimate value of SNR by the known account formula of SNR. Simulation results show that it is correct and feasible.