Disclosed is a leak-proof device for a water inlet valve. A control valve is installed in a valve body for opening and closing a water inlet channel and a water outlet channel. An outer water tank and a leak-proof water tank are installed on the valve body. An inner water tank is disposed in the outer water tank, with the height of the inner water tank being lower than that of the outer water tank. The leak-proof water tank is in communication with the inner water tank via a water-passing channel A lever is pivotally connected to the valve body. Two ends of the lever are connected with an outer float and an inner float. The inner float is provided with a plug that is movable to block the water-passing channel. The leak-proof float is connected to the control valve.