Based on high intensity laser systems theory and self-focusing research, the nonlinear medium under the beam transmission process was described using the beam propagation method and ray tracing method. Besides, it was found that some ways were suitable for nonlinear medium, such as Adams method under the ray tracing method and recovery algorithm based on gradient information of intensity distribution. Finally, the simulation results revealed the relationship between the light intensity and these factors, including lens thickness, the refractive index of medium, the lens curvature radius and the radius of the incident beam. And combined with optical design software, it not only reflected the relationship between the product of the refractive index and the light intensity and the focus position changes, but also the results of image quality intuitively through the data of spot diagram. And two kinds of main optical methods, the ray tracing method and the beam propagation method, were made for the comparative analysis. According the simulation results, it could be determined that bits of the system was easily affected by self-focusing, so the size of certain parameters could be improved, the adverse effect could be reduced and eliminated, and an optimal method which was suitable for strong laser system could be found.