The present invention relates to an improved draught fan filtering device which comprises a fixing support. The fixing support comprises an inner support body and an outer support body; an inner flange and an outer flange are connected to the rear end of the inner support body and the rear end of the outer support body respectively; a sound arrester is connected in a gap between the inner flange and the outer flange; a draught fan is connected in the sound arrester; the periphery of the inner support body is wrapped by a mesh isolation layer; connecting frames are arranged between the two sides of the inner support body and the two sides of the outer support body and between the front ends of the inner support body and the outer support body and are provided with buckles; and filtering cotton is fixed in the buckles. The improved draught fan filtering device has the advantages that the situation that the filtering cotton is sucked in is avoided through the mesh isolation layer, and the filtering cotton can be fixed by the buckles and is not likely to loosen or disengage or move freely; and furthermore, the filtering cotton can be added at will according to the number of the buckles, the filtering cotton can be replaced or added in the operation process of the improved draught fan filtering device, and difficulty is lowered.