The invention provides an anti-blocking drum screen which comprises a main shaft, a cross beam, cross beams, keel steel frames, drum spokes, upper-layer screen sheets and an outer-layer main screen mesh. To solve the problem that a conventional drum screen has screen blocking in ore pulp screening, by employing the probability screening principle, the upper-layer screen sheets parallel to the axisof a drum are arranged in the drum screen in the circumferential direction at equal intervals. The apertures of the upper-layer screen sheets are several times greater than the particle size of the outer-layer main screen mesh, and the upper-layer screen sheets have the main functions of preventing a large number of materials from being stacked on the screen surface of the outer-layer main screenmesh at the same time, so that the screen hole blocking problem in the ore pulp screening is solved.