In this paper, first, the pulse pressure signal at the entrance of a single-cylinder engine muffler was measured. Next, based on the physical structure of the muffler, a simulation model of the muffler was constructed. Then, by considering the exhaust characteristics of the single-cylinder engine, a method was proposed to determine the critical conditions according to the effective pulse pressure. Moreover, the distribution of pressure loss in the muffler was simulated based on the computational fluid dynamics （CFD） , and the simulated results were used to discover the parts with large pressure loss in the muffler, with some measures being taken to improve the internal structure of the muffler. Finally, in the same operation conditions, the entrance pressure signal of the improved muffler was measured and simulated. The results indicate that the pressure loss in the improved muffler falls remarkably and distributes more regularly.