The sound proof unit is widely used in outdoor or indoor places requiring protection and noise reduction with special requirements for environmental protection. It is mainly composed of standard unit, sound proof enclosure, air inlet and exhaust noise reduction device and exhaust noise reduction device. Its main characteristics are that the sound proof enclosure is provided with sound insulation and sound absorption layer, the air inlet and exhaust channels are provided with noise reduction treatment, and the exhaust adopts a combination of industrial and residential silencers to reduce the noise in high and low frequency bands. The noise of standard sound proof unit is generally 78-85db (a), and that of super sound proof unit is generally 70-78db (a). The super sound proof unit is realized by adopting more strict control measures for noise emission on the basis of the standard sound proof unit, such as labyrinth air inlet and exhaust channel design. Super sound proof units are generally large in size, and the manufacturing cost is much higher than that of standard sound proof units. Sound proof units and super sound proof units are usually operated, maintained and overhauled outside the sound proof enclosure.