Resistance coefficient is an important indicator to measure the aerodynamic performance of the muffler. The impedancecompound muffler structure and its characteristics were analyzed, and the muffler model was set up. By using three dimensional computational fluid dynamics (CFD), the resistance coefficient was calculated and compared with the actual measurement, which proved the feasibility of the calculating method. This paper also analyzed the influence on the resistance coefficient of muffler of the air flow rate and cavity length, perforated ratio, perforated diameter. Obtained at the same velocity, the muffler resistance coefficient is smaller, and the smaller the pressure loss, the better the aerodynamic performance. This provides a reference for optimum design of muffler.