The invention relates to a multistage filtering deduster. The multistage filtering deduster comprises a shell, an ash bucket, a cover plate and a horizontally arranged separator plate mounted at the inner side of the shell, the separator plate divides the inner side of the shell into an upper part and a lower part which are not communicated, the ash bucket is mounted below the shell, the cover plate is mounted above the shell, a mixed flow chamber is formed among the shell, the ash bucket and the separator plate, a flow collecting chamber is formed among the shell, the cover plate and the separator plate, the shell is provided with an air inlet communicated with the mixed flow chamber, and the shell is provided with an air outlet communicated with the flow collecting chamber; the separatorplate is provided with an axially-vertically-arranged inner cylinder placed in the mixed flow chamber, the inner cylinder is rotatably connected with the separator plate, and a flow guiding chamber is formed at the inner side of the inner cylinder; the inner cylinder is provided with a special-shaped filter bag with opened top and bottom, placed below the inner cylinder, the vertical position ofthe special-shaped filter bag corresponds to the position of the air inlet, and the inner cylinder is provided with a pressurization fan placed at the inner side of the special-shaped filter bag; andthe separator plate is provided with a plurality of vertically-arranged micro-porous filter bags placed in the flow guiding chamber, and the upper ends of the micro-porous filter bags upwards go through the separator plate and are connected with the separator plate.