The internal structure of the box is similar to that of a bag filter, which filters the paint mist in the air based on the principle of filtration. The filtering medium consists of multiple layers of honeycomb paper and one layer of coarse filter cotton. During the process of air carrying paint mist passing through the filter medium, the sticky paint mist is adhered by multiple layers of honeycomb paper, while the small particles with low viscosity are carried by the air through the honeycomb paper layers and filtered by the filter cotton. The filter medium that changes from sparse to dense along the main direction of the air flow can prevent the windward side from being quickly clogged by paint mist, and the final filter cotton can also ensure a high filtration efficiency.