The invention relates to a testing device for simulating operation of filling CO2 into a mine gob area for preventing and extinguishing fire, and aims at the situations that coal self-combustion is severe in the mine excavation process, the difficulty is large in eliminating coal self-combustion and the fire is not easy to extinguish. The testing device adopts a mechanical structure and utilizes technologies of heating, measuring the temperature, controlling the temperature, feeding air, returning air, inputting CO2, controlling CO2, sampling, measuring and measuring by using a gas chromatograph and calculating by using an information computer so as to obtain the rules of fire fighting with CO2, and the on-site coal mine fire extinguishment can be well performed. The testing device is advanced in design and reasonable in structure, integrates on-site simulation, information acquisition and treatment, can accurately obtain data of fire extinguishment with CO2, and is an ideal testing device for simulating operation of filling CO2 into the mine gob area for preventing and extinguishing fire.