The results show that the factory resistance muffler has better effect in eliminating medium frequency and high frequency noise, while impedance composite muffler has poor effect in eliminating low frequency noise. The noise reduction amount is related to the structure of muffler, cross-section shape and area of air passage, air flow velocity, muffler length, type, density and thickness of sound absorption material It also has a great influence on the sound elimination effect. The protective material can be made of fiber cloth or perforated plate with good permeability, and the perforated plate for the cover is generally made of thin plate, aluminum plate, steel plate, etc. In order to give full play to the sound absorption performance of sound absorption material, the perforation rate of perforated plate should be more than 20% of 3-10 mm. In general, the wind speed of the resistive muffler should be 8m / s lower than that of the wind speed, and should not be greater than 12m / s. when the wind speed of the microporous plate muffler is larger (15 ~ 20m / s), the wind resistance is larger. The common sound absorption materials include glass fiber, low carbon steel wire mesh, felt, etc. in the single straight pipe muffler, the high frequency sound decreases obviously with the increase of the passage area. In this case, because the frequency is higher than a certain value, which does not conform to the propagation law of plane wave, the sound wave does not contact with the sound absorption material, and the sound attenuation effect is reduced.