The drum filter adopts a stainless steel filter screen as the filtering layer. The liquid to be filtered enters the filtering chamber from one side of the filter. Due to the gravity of the liquid itself, it automatically filters out impurities through the filter screen. At the same time, the filter screen rotates in a circular motion driven by the driving motor, and the liquid flows along with the rotation of the filter screen itself after entering the filtering chamber, thereby achieving maximum contact with the filter screen and completing the filtration. The filtered fibers or solid particles adsorb onto the inner surface of the filter screen to form an impurity layer, and a set of high-pressure nozzles are installed on the outer wall of the filter screen. When the filter screen carries the fiber layer to the nozzle position, the fiber layer automatically separates from the inner wall of the filter screen under the impact of the high-pressure nozzles or compressed air and is collected in the sewage collection tank. Then the impurities are separated and discharged through the sewage pipeline of the collection tank and the filtered liquid.