The invention relates to an automatic drainage system for construction or reinforcement construction of a stilling basin bottom plate in hydraulic engineering. The automatic drainage system comprises a water pump and water collection pipes. The water pump is provided with a PLC control panel, a water inlet pipe and a water outlet pipe. The water inlet pipe is provided with a plurality of branched water inlet pipes which are connected with water pumping pipes correspondingly. The water pumping pipes are connected to the corresponding water collection pipes. The water collection pipes are arranged in a seepage place. An inductor is arranged at an upper opening of each water collection pipe. Floating bodies rises along with the water level to get close to the corresponding inductors, and then a water pumping instruction is sent to the water pump. The water outlet pipe is provided with a detector. When detecting that the water outlet pipe stops water supply or the water supply is lower than a set value, the detector sends out a water pump turn-off signal. The stilling basin bottom plate is constructed or reinforced and maintained ty means of the scheme, the manufacturing cost can be reduced, and the construction time can be shortened. Moreover, upstream stored water does not need to be emptied, and losses of water resources are reduced.