The invention provides a testing device of desorption and seepage of steam driven coal mass methane. The testing device comprises a vacuumizing system, a gas injection system, a desorption and seepage system and a gas metering system, wherein the vacuumizing system comprises a vacuum pump and a vacuum container; a gas inlet of the vacuum pump is connected with a gas outlet of the vacuum container through a first gas pipe; a vacuum meter and a first stop valve are arranged on the first gas pipe along the flowing direction of gas; the gas injection system comprises a methane gas tank; the methane gas tank is connected with the desorption and seepage system through a second gas pipe; the second gas pipe is provided with a high-pressure meter, a first decompression valve, a low-pressure valve, a first pipeline boosting pump, a second stop valve, a check valve, a steam generation mechanism, a pressure regulating valve, a third stop valve and a first pressure meter in sequence along the flowing direction of the gas. The testing device provided by the invention is convenient to operate, small in working amount, rapid and accurate to measure, and high in experiment performance, and provides experiment and theoretical research for penetration rate and penetration amount of coal seam gas.