Abstract: The weighted nonlinear least squares iterative fitting method is an important method to solve the -particle spectra. The appropriate spectrum peak shape function model and the initial values of the parameters are the key to the nonlinear least squares iterative fitting. Based on the shaping mechanism of -ray spectrum, a kind of -ray spectrum peak shape function was established, and the method of determining the initial values of the peak shape function based on the moment estimation was proposed. The mathematical statistics, the mean, variance and third-order central moments of the peak shape function and the discrete spectral peak data were calculated respectively. The initial values of the parameters were obtained by the established equations. The radon daughters alpha spectra detected by a continuous aerosol detector and 238Pu surface-source -energy spectra detected by a low-background -ray spectrometer were used to test the peak shape function model and the initial values acquisition method. The results show that the peak shape function model can be well applied from high-degree overlapping to low-degree overlapping. The initial values of the parameters of the peak shape function obtained by the moment estimation method can make the peak shape function well fit the alpha spectrum data. The method has strong practicability in the computer automatic analysis of alpha spectrum.