Today, motorcycles are one of the main noise pollution sources in Asia. In addition, the design of motorcycle muffler is closely related to how noise is made as the regulation is getting crucial these years. Therefore, TL (Transmission Loss) is an important index to evaluate characteristics of a muffler, but conventional trial and error method results in time wasting muffler tests. In this paper, in order to shorten the development period, Ricardo WAVE software is used to analyze the muffler TL of a 400cc motorcycle manufactured by a domestic company. Because of the complex design inside the muffler, simple elements constructing the muffler like single expansion chamber, non-coaxial insert expansion chamber and sound absorbing materials are investigated at first. There are three goals in this research. First, this research is mainly for verifying the accuracy of Ricardo WAVE that simulates characteristics of simple muffler. Second, the verification of a complex motorcycle muffler is executed. In the end, sound absorbing material housing and connecting ducts are discussed for the influence of TL on a motorcycle muffler. The results show that Ricardo WAVE is able to simulate both simple muffler and complex motorcycle muffler. And it is found that when the sound absorbing materials housing is attached to the model, TL in the range of low frequency would be changed. Moreover, the results of TL turn out to be increased under a low frequency range while attaching connecting ducts to the model.