The invention relates to an electromagnetic pilot-operated diaphragm valve. A water through opening is arranged at a water inlet and a water outlet, and a valve cover is arranged on a control opening; and a diaphragm is arranged between the valve cover and the control opening and can close the water through opening. A water pressure balance cavity is formed between the diaphragm and the valve cover, and the valve cover is provided with a pressure releasing slot which is provided with an electromagnetic valve. The bottom of the pressure releasing slot is provided with a first pressure releasing hole communicated with the water pressure balance cavity, and the diaphragm is provided with a jet orifice. A protruding pole is arranged on the inner surface of the valve cover, the middle part of the diaphragm is fixed on the protruding pole, a second pressure releasing hole is arranged in the protruding pole, and a valve plug of the electromagnetic valve can close the second pressure releasing hole. The water intake aperture of the diaphragm ranges from 15 mm to 20 mm, and the ratio of the areas of the water inlet and the water outlet ranges from 1.5 to 2. The invention can greatly reduce the volume of the whole valve, reduce materials, lower the cost, greatly shorten pressure releasing passages, speed up opening and closing, accomplish normal opening and normal closing at the extremely low water pressure of 0.01 MPa and reduce water hammer, etc.