In this paper based on the characteristics of millimeter wave radiation signal for wavelet transform, non-negative wavelet coefficient is used as the wavelet coefficient of the signal. For a given threshold value, the wavelet coefficient which is smaller than the threshold is set zero and the wavelet coefficient which is larger than the threshold is set the difference between the coefficient and a constant a.The method for valuing a is inferred by the variance function of signal, and the experiments show that it has good ability of removing the noise in MMW target radiation signal.