The work presented in this paper focuses on the usability testing for the Open-Modelica. The modeling and simulation of the BMR450 DC-DC converter is also considered. The main emphasis which was reported here consists of four different models and the comparison between the simulation results. One logic block model and one electrical model are built on the Modelica platform, while the control group with one logic block model and one electrical model are based on Matlab platform. Through analyzing and comparing the characteristics of the simulation results from different models, I get the conclusions on the usability of the Open-Modelica software. At the meantime, we also fix the bug in one element model, and apply the multi-value capacitor theory for optimize the output characteristic of the converter.