The invention discloses an overflow safety valve. The overflow safety valve comprises a liquid inlet connector with a liquid inlet hole, a spring seat, a reset spring and a valve element component which is movably arranged in a valve casing and used for controlling opening and closing of the liquid inlet hole. The spring seat is provided with a first boss inserted into the reset spring and a second boss which makes contact with the valve element component and is shaped like a sphere. According to the overflow safety valve, the movable valve element component is arranged inside the valve casing, the valve element component can be used for controlling passing and breaking of an oil passage from the liquid inlet hole to a liquid draining hole, large-flow overflowing can be achieved when the valve element component is far away from the liquid inlet connector, the flow of the safety valve is greatly increased, rapid overflowing in short time can reduce axial displacement of the valve element component, reduction of the axial displacement of the valve element component can reduce axial deformation of the reset spring, and pressure fluctuation can be reduced finally; the two bosses are arranged on the spring seat which is only subjected to axial force, radial interference does not exist, the situation that the reset spring is jammed or bent and deformed due to the axial force is prevented, and the stability of the spring seat is improved.