In order to alleviate the ill-posed problem of the ill-conditioned equation, the regularization algorithm combined with averaging method is used to retrieve the aerosol particle size distribution. In this method, the selection of the optimal average interval is crucial. According to the spectral of LED, fourteen wavelengths for the LEDs are selected, and different optical parameter combinations are set. By the retrieval of multiple sets of original volume concentration distribution and error statistics, the optimal average interval of each optical parameter combination is obtained. The retrieval simulations of logarithmic-normal volume concentration distribution were completed. The simulation results show that when using a combination of ten backscatter and ten extinction coefficients, the reconstructed monomodal distribution has the best fitting effect, and the relative error of effective radius and volume are the smallest. And when using a combination of six backscatter and six extinction coefficients, the reconstructed bimodal distribution has the best fitting effect, and the relative error of effective radius and volume are the smallest.