The present invention discloses a filtering device used for removing impurities in a mixture of biological diatomite, which relates to the technical field of sewage treatment. This device includes a plurality of deflectors evenly distributed in multiple layers in the vertical direction. Each deflector includes a shell and a top plate. There is a filter unit symmetrically arranged on the left and right sides of each deflector. The top of the shell is covered with a top plate hinged with the depressed plate. The bottom of the shell is provided with water inlets which communicate with the shunt pipe, and the upper parts of the left and right side walls of the shell are provided with overflow ports. The shell also has a plurality of diversion folding plates located below the overflow ports and vertically staggered and distributed on the left and right side walls. The filter unit includes an inclined water guiding groove and a filtering plate.