The invention discloses a preparation method of an active covering plate for synchronously controlling nitrogen and phosphorus release of bottom mud. The preparation method comprises the following steps: (1) naturally air-drying sludge of a water purification plant, and calcining to obtain a sludge block; (2) the sludge blocks are subjected to mechanical crushing and mechanical vibration screening, and the aluminum-based phosphorus locking agent is prepared; (3) adding the aluminum-based phosphorus locking agent, cement, zeolite and water into a stirrer according to a ratio, uniformly mixing, and standing to obtain a base material; (4) the base material is added into a mold frame to be pressed; (5) after compression molding, standing and demolding to obtain a cover plate; and (6) standing the cover plate finished product under a natural open air condition for engineering application. The active covering plate prepared by the invention not only can synchronously control the release of nitrogen and phosphorus in bottom mud, but also has the advantages of washing resistance, good water permeability, high water retention and the like, and solves the problems of non-uniform covering, flood washing loss and the like of a granular covering material; the prepared active covering plate can be recycled, cyclic utilization of resources is promoted, meanwhile, the process is simple, operation is convenient, and the cost is low.