An apparatus and method for testing the performance of a safety valve. The apparatus includes an accumulator including at least one electric heater for heating a predetermined amount of water in the accumulator, and storing steam produced by the electric heater, a test vessel storing the steam supplied from the accumulator, and providing steam at a test pressure to a safety valve, the steam being supplied after controlling flow rate and pressure, a condensing tank storing demineralized water to be supplied to the accumulator, and condensing and collecting the steam discharged from the safety valve, and a water-supply pump supplying the water stored in the condensing tank to the accumulator.