The transmission loss is one of the important characteristics to appraises the muffler performance. But in the experiment, it should been pay attention to the acoustic source stability and sound wave reflection questions.In this article summarized some differences which the insertion loses and transmits loses, Simultaneously pointed out the merits of application transmission loss test noise elimination performance，And for avoided the sound reflection proposed one new transmission loss test way. Discussed the transmission loss value change situation when the muffler be inputed different intensity sound pressure, which through the massive experiments.