A single-cycle refrigerating system, comprising a compressor, a one-way valve, a condenser, an electric valve, a capillary tube and an evaporator; wherein the compressor, the one-way valve, the condenser, the electric valve, the capillary tube and the evaporator are connected in turn, one end of the evaporator is connected with the capillary tube, and the other end of the evaporator is connected with the compressor; the electric valve is connected with an exhaust port of the compressor via a pressure relief channel; wherein the electric valve comprises a valve seat, an electric motor and a valve cap; an inlet, a pressure relief port and an outlet are set on the valve seat, wherein the pressure relief port and the outlet are located on the upper surface of the valve seat; the valve cap is covered above the valve seat; the electric motor is fixedly set on the valve cap, and the electric motor includes a stator and a rotor, wherein the stator is set on the outer surface of the valve cap, and the rotor is set in the intracavity of the valve cap; the central part of the rotor is provided with a mandrel, and the rotor may rotate around the axis of the mandrel; the lower end of the mandrel is fixedly provided with a valve core that is opened with a pressure-relief diversion slot and a through slot, and the lower surface of the valve core contacts the upper surface of the valve seat, the pressure-relief diversion slot is opened on the lower surface of the valve core, and the through slot penetrates through the valve core along the thickness direction of the valve core; when the valve core is rotated, the electric valve may change among a cutoff state, an open state and a pressure relief state; in the cutoff state, the pressure-relief diversion slot and the through slot of the valve core are not in communication with the outlet of the valve seat, the pressure relief port and the outlet are both blocked by the valve core, and the inlet is not in communication with the outlet or the pressure relief port; in the open state, the through slot of the valve core is exactly located above the outlet, and the pressure relief port is blocked by the valve core, the through slot of the valve core is in communication with the outlet of the valve seat, the inlet is in communication with the outlet via the through slot of the valve core, and the pressure relief port is not in communication with the inlet or the outlet; in the pressure relief state, the pressure-relief diversion slot of the valve core is exactly located above the outlet and the pressure relief port, and the through slot is blocked by the valve seat, the pressure-relief diversion slot of the valve core and the outlet of the valve seat are both in communication with the pressure-relief port, and because the pressure-relief diversion slot is located on the lower surface of the valve core and does not penetrate through the valve core, the pressure-relief diversion slot only communicates the pressure relief port and the outlet internally, thus the inlet is not in communication with the outlet or the pressure relief port; the electric valve is adjusted to the open state as the compressor is started, and the electric valve is adjusted to the pressure relief state or the cutoff state in the stage that the compressor is stopped.