The invention discloses an insulation breakdown based device and method for testing liquefaction temperature of insulating gas. The device comprises a thermostat, a constant-volume bottle, an electrode pair, a gas preparation device, a liquid phase detection device and a data monitoring and processing unit, wherein the constant-volume bottle is arranged in the thermostat, and a thermometer and a piezometer are arranged in the constant-volume bottle; the electrode pair is arranged on the wall of the constant-volume bottle, discharge ends of the electrode pair are located in the constant-volumebottle, and the two ends, located outside the constant-volume bottle, of the electrode pair are connected with a high-voltage power supply to form a loop; the liquid phase detection device comprises an optical fiber scene processing unit which is communicated with the constant-volume bottle; the gas preparation device is communicated with the constant-volume bottle; the thermometer, the piezometer, the thermostat, the gas preparation device and the liquid phase detection device are communicated with the data monitoring and processing unit through signal lines respectively. According to the testing device, the problem of approximation based on an ideal gas equation calculated value can be solved, and the liquefaction temperature of the insulating gas can be tested in situ and verified.