An ejector for use in a refrigeration system, comprising: a mixing chamber comprising a mixed fluid outlet; a high-pressure fluid passage extending from a high-pressure fluid inlet to the mixing chamber, a flow valve for controlling a flow rate being disposed in the high-pressure fluid passage; a suction fluid passage extending from a suction fluid inlet to the mixing chamber; and an elastic diaphragm disposed in the high-pressure fluid passage, wherein a closed cavity is on a first side of the elastic diaphragm, and the high-pressure fluid passage is on a second side of the elastic diaphragm; the closed cavity is filled with fluid; and the elastic diaphragm is associated with the flow valve so that an opening degree of the flow valve varies in response to a change in a pressure difference across two sides of the elastic diaphragm; characterised in that the ejector comprises a thermal bulb disposed upstream of the flow valve, in the high-pressure fluid passage or outside the high-pressure fluid passage, wherein the thermal bulb is in communication with the closed cavity, and the thermal bulb is filled with fluid; and the elastic diaphragm is associated with the flow valve such that when the pressure of the high-pressure fluid is lower than the desired pressure, the opening degree of the flow valve will decrease, thereby increasing the pressure of the high-pressure fluid; and when the pressure of the high-pressure fluid is higher than the desired pressure, the pressure of the fluid in the closed cavity is lower than that of the high-pressure fluid, and the opening degree of the flow valve will increase, thereby decreasing the pressure of the high-pressure fluid. a mixing chamber comprising a mixed fluid outlet; a high-pressure fluid passage extending from a high-pressure fluid inlet to the mixing chamber, a flow valve for controlling a flow rate being disposed in the high-pressure fluid passage; a suction fluid passage extending from a suction fluid inlet to the mixing chamber; and an elastic diaphragm disposed in the high-pressure fluid passage, wherein a closed cavity is on a first side of the elastic diaphragm, and the high-pressure fluid passage is on a second side of the elastic diaphragm; the closed cavity is filled with fluid; and the elastic diaphragm is associated with the flow valve so that an opening degree of the flow valve varies in response to a change in a pressure difference across two sides of the elastic diaphragm; characterised in that the ejector comprises a thermal bulb disposed upstream of the flow valve, in the high-pressure fluid passage or outside the high-pressure fluid passage, wherein the thermal bulb is in communication with the closed cavity, and the thermal bulb is filled with fluid; and the elastic diaphragm is associated with the flow valve such that when the pressure of the high-pressure fluid is lower than the desired pressure, the opening degree of the flow valve will decrease, thereby increasing the pressure of the high-pressure fluid; and when the pressure of the high-pressure fluid is higher than the desired pressure, the pressure of the fluid in the closed cavity is lower than that of the high-pressure fluid, and the opening degree of the flow valve will increase, thereby decreasing the pressure of the high-pressure fluid.