The outer frame of the air filter is an aluminum alloy frame or a stainless steel frame, and a gold-aluminum small aperture multi-layer folded net is built in. The filter material is composed of multi-layered crosswise and cross-shaped waveforms, and the double-sided and cross-steel bars are used for strong support and support functions. To increase its sturdiness, the structure of the multi-layer filter can increase the filtration time and is more economical. The role of the device is to block large particles of dust and debris, can be used repeatedly, high permeability, low pressure loss. Each layer inside and outside the aperture size is different, blocking different sizes of debris long life.