The main sound source of motorcycle noise is engine exhaust noise in the paper. Installing muffler can effectively reduce the exhaust noise, in the other word, if the acoustic performance of muffler can be improved, exhaust noise of engine will effectively be suppressed. Based on the FEM, establishing the acoustic simulation model, the performance of muffler relates to acoustic is studied. Based on muffling theory, the optimal projects of the interior structure for muffler are proposed. Through doing experiments of insertion loss for muffler and the pass-by noise for motorcycle, these confirmed that the improved muffler can reduce the motorcycle’s noise.