The invention belongs to the field of automatic drainage, and relates to an automatic drainage system. The system includes a water storage tank. The wall of the water storage tank is sequentially provided with a water inlet pipe, an emergency water outlet pipe, a first liquid level meter, a second liquid level meter, a third liquid level meter and drainage pumps. The height of the first liquid level meter is same as that of the emergency water outlet pipe, the second liquid level meter is located in the middle between the first liquid level meter and the third liquid level meter, and the drainage pumps include the first drainage pump and the second drainage pump which are located on the bottom surface of the water storage tank and connected with a power supply box and a control system. Thefirst liquid level meter, the second liquid level meter and the third liquid level meter are all connected with the power supply box and the control system. The system is reasonable in structure design, the action of the immovable drainage pumps can be controlled according to different water level conditions, energy consumption is reduced to a certain extent, the emergency water outlet pipe is arranged, and when the water level is too high, water can be directly discharged to a safe position by the emergency water outlet pipe through pressure caused by the water level difference.