The exhaust pollution from the vehicle has become one of the important reasons for environment pollution. With the advancement in automobile industry, the exhaust muffler has been paid attention to improve the performance of engines. Computational Fluid Dynamics (CFD) method is used to analyze the aerodynamic performance and effect which the internal flow field has on the performance of the muffler. With this method, the pressure distribution in the muffler is simulated and the pressure loss was predicted. Resistance muffler research relates with the fields of acoustics, fluid dynamics, heat transfer and mechanical design. The experiment results verify that, the assembly performance of the muffler is better.