When the bag filter works, the dust-containing gas enters the dust hopper of the dust collector from the lower part of the dust collector box. Because of the sudden enlargement of the airflow cross-section area and the decrease of the flow velocity, some of the coarse and denser particles in the dust-containing gas are settled by gravity and directly fall into the dust hopper of the dust collector with fine particle size and small density. The particles enter the filter chamber where the filter bags are distributed. Through the inertia, collision, screening, interception and electrostatic adsorption on the surface of the filter bags, the particles adhere to the surface of the filter bags and form a dust layer. The clean gas filtered and purified is discharged by the exhaust pipe through the upper air chamber.