In the technology of particle size measurement based on forward light scattering， the inversion algorithm is one of the key issues affecting the accuracy of the measurement results. As a relatively new adaptive global optimization algorithm， genetic algorithm parameters optimization and objective function design determine the accuracy of inversion results of particle size distribution. In this paper， the setting of relevant parameters of genetic algorithm is discussed， and the numerical simulation results show that the algorithm is effective in the inversion of the particle size distribution of polydisperse particle system. The measurement and inversion calculation of polystyrene standard particles size distribution were carried out. The results prove that the optimized genetic algorithm which the genetic iteration is 3 200， population scale is 50， crossover operator is 0.7， mutation operator is 0.002 and the weight coefficient of fairing factor is $\mathrm{1.5}\times {\mathrm{10}}^{-\mathrm{5}}$ has good stability and noise immunity， and can effectively reconstruct the particle size distributions.