Clean rooms are classified according to indoor cleanliness, air flow form, control objects, indoor net height and structural characteristics. According to the classification of indoor cleanliness, it can be divided into 1 level, 10 level, 100 level, 10 000 level and 10 000 level. According to the form of air flow, it can be divided into unidirectional flow, vector flow and turbulent flow. According to the control object, it can be divided into industrial clean room and biological clean room. The former takes the suspended dust in the air as the control object, while the latter takes the suspended biological particles (microorganisms) as the control object. According to the indoor height, it can be divided into low-level clean room and high-level clean room. The net indoor height of the former is less than 3m, and that of the latter is more than 3m.