The invention discloses an electronegative gas injection device capable of maintaining the dynamic pressure, which comprises a gas pressure maintaining bin, wherein the gas pressure maintaining bin isinternally provided with a piston, the piston is connected with a screw driving device, the screw driving device is connected with a stepping motor, the gas pressure maintaining bin is provided witha gas injection port, a gas outlet and a gas pressure meter, the gas injection port and the gas outlet are respectively provided with electromagnetic valve control. The gas pressure maintaining bin isprovided with a piston position detection device. The gas pressure meter, the electromagnetic valve control, a control unit of the stepping motor and the piston position detection device are connected with a control system. The gas outlet is connected with a vacuum chamber which generates plasmas, and the gas injection port is connected with an electronegative gas bottle. The electronegative gasinjection device can dynamically maintain the gas pressure and maintain the stable release speed of an electronegative gas, thereby ensuring the accuracy of a physical experiment result, and solving aproblem that the gas pressure drops continuously during the release of the electronegative gas.