The utility model relates to a device for replenishing gas in an ultrahigh-pressure experiment process. The device comprises a high pressure storage tank kettle body, a gas input pipe, a stable pressure decompressing gauge, a gas output pipe and a pressure indicator, wherein the top end of the high pressure storage tank kettle body is provided with the gas input pipe and an air outlet pipe; the initiating end of the gas input pipe is provided with a joint capable of being connected with an increasing pump, and the gas input pipe is provided with an air inlet valve; the air outlet pipe is provided with an air outlet valve, the air inlet end of the stable pressure decompressing gauge is connected with the air outlet valve, and the air outlet end of the stable pressure decompressing gauge is connected with the gas output pipe; the tail end of the gas output pipe is provided with the joint, the top end of the high pressure storage tank kettle body is provided with a through hole, and a pressure sensor is arranged in the through hole in an encapsulation manner; the side surface of the high pressure storage tank kettle body is provided with the pressure indicator, and the pressure sensor is connected with the pressure indicator through a signal line. The device provided by the utility model has the advantages that the gas can be stably replenished to a high temperature and high pressure reaction kettle, the application pressure range is wide, and the device is particularly suitable for replenishing gas containing trace impurity in an ultrahigh-pressure corrosion experiment process.