A relief valve comprising: a valve seat, the valve seat is formed with a cavity therein, a water outlet passage and a pressure relief passage are provided on the bottom of the valve seat, both of which communicate with the cavity, the centre of a bottom surface of the cavity is provided with an upward protrusion, and the pressure relief passage runs through the upward protrusion; the valve body is fixed inside the cavity, a sealing ring is disposed between the peripheral surface of the valve body and the inner wall of the cavity for sealing the relief valve; a water inlet passage communicating with the cavity is provided on the top of the valve body, the bottom of the valve body is formed with a recess; and a sealing plate, made of flexible material, is disposed inside the cavity and positioned under the valve body, a gap is formed between the peripheral surface of the sealing plate and the inner peripheral wall of the cavity; characterized in that: a plurality of apertures are provided in an inner peripheral wall of the recess each communicating with the outer peripheral surface of the valve body, a downward protrusion is provided at the centre of the recess, the water inlet passage runs through the downward protrusion; and a plurality of elastic portions protruding downward is provided on the bottom surface of the sealing plate, the bottom of each elastic portion is supported on the bottom surface of the cavity to ensure that the sealing plate is always separated from the inlet of the water outlet passage; in a normal situation, the elastic portions separate the bottom surface of the sealing plate from the inlet of the pressure relief passage; when water flows through the water inlet passage, under the water pressure, the centre of the sealing plate is forced to deform and sink to block the inlet of the pressure relief passage. a valve seat, the valve seat is formed with a cavity therein, a water outlet passage and a pressure relief passage are provided on the bottom of the valve seat, both of which communicate with the cavity, the centre of a bottom surface of the cavity is provided with an upward protrusion, and the pressure relief passage runs through the upward protrusion; the valve body is fixed inside the cavity, a sealing ring is disposed between the peripheral surface of the valve body and the inner wall of the cavity for sealing the relief valve; a water inlet passage communicating with the cavity is provided on the top of the valve body, the bottom of the valve body is formed with a recess; and a sealing plate, made of flexible material, is disposed inside the cavity and positioned under the valve body, a gap is formed between the peripheral surface of the sealing plate and the inner peripheral wall of the cavity; a plurality of apertures are provided in an inner peripheral wall of the recess each communicating with the outer peripheral surface of the valve body, a downward protrusion is provided at the centre of the recess, the water inlet passage runs through the downward protrusion; and a plurality of elastic portions protruding downward is provided on the bottom surface of the sealing plate, the bottom of each elastic portion is supported on the bottom surface of the cavity to ensure that the sealing plate is always separated from the inlet of the water outlet passage; in a normal situation, the elastic portions separate the bottom surface of the sealing plate from the inlet of the pressure relief passage; when water flows through the water inlet passage, under the water pressure, the centre of the sealing plate is forced to deform and sink to block the inlet of the pressure relief passage.