The thermal mass Flowmeter is composed of sensor and signal analysis, processing and control unit. One part of the sensor measures the temperature, while the other is used for heating. The former monitors the temperature value of the actual process, while the latter maintains a constant temperature value so that it is always higher than the actual process temperature and maintains a constant temperature difference with the process temperature. The greater the mass flow rate of the gas, the greater the cooling effect, and the greater the energy required to maintain the differential temperature. Therefore, the mass flow rate of the measured gas can be obtained by measuring the energy of the heater.