Study of high frequency switching power has focused on Inductor-Inductor-Capacitor(LLC) resonant converter recently, and simulation with Personal Simulation Program with Integrated Circuit Emphasis(PSPICE) for switching power has become an important computer-aided analysis and design measure．To solve the non-convergence problems encountered in using the PSPICE simulator for switching power DC analysis and transient analysis, experiments were carried out on how to improve the convergence problem about the LLC PSPICE circuit simulation. Five improved effective methods were listed. Various programs proposed for the design optimization of three parameters of the LLC resonant converter were compared, and the multi-parameter optimization method using PSPICE was presented and validated. Experiments results show that the reasonable use of PSPICE can obtain more satisfactory results than using other methods (software) in the design of switching power supply.