The primary, middle and high efficiency filters refer to the pre-filtration, intermediate filtration and terminal filtration of the air filter. It is the key equipment in the purification air-conditioning system. It provides clean air for the clean room through the step-by-step filtration of the filter to ensure its reliable operation. According to the filtration efficiency: initial efficiency (G one to G four), medium efficiency (F five to F nine), high efficiency (H thirteen to H fourteen). The primary air filter is generally used for the pre-filtration of ventilation filtration, and its precision is greater than five microns. The medium-efficiency filter is generally used as an intermediate filter for purifying the air-conditioning system, and its precision is generally one to five microns. The high-efficiency filter is generally used as the end filter of the clean room, and its precision is mainly used to intercept particles below one micron. Structural forms include clapboard, no clapboard, large air volume, super-efficient and so on. The performance of the primary, middle and high efficiency filters directly affects the air purification effect of the purification air conditioning system and the cleanliness level of the room. Therefore, purifying the air conditioning system must choose the appropriate air filter.