The bag filter is a dry filter device. It is suitable for capturing fine, dry, non-fibrous dust. The filter bag is made of woven filter cloth or non-woven felt, and the dust-containing gas is filtered by the filtering effect of the fiber fabric. When the dust-containing gas enters the bag filter, the dust with large particles and heavy specificity will be affected by gravity. The effect settles down and falls into the ash hopper. When the gas containing finer dust passes through the filter material, the dust is blocked, so that the gas is purified.