The A new Electro-Thermal Modelling is built for the infrared light source of non-dispersive infrared sensing technique for CO2 measurement. To verify the effectiveness of our proposed NDIR electro-thermal modelling, a NDIR CO2 measuring system is built and installed inside a gas chamber for CO2. The measuring module includes a light source at one end of an optical tube with 4 cm long and the infrared sensor connected to the other end of the optical tube; respectively. A period heating of infrared light source is applied to give infrared radiation in gas analyzer which operates based on the non-dispersive infrared sensing. For the conventional technique of constant periodic heating of infrared light source, an CO2 infrared sensor with a specific wavelength filter is used to give a signal corresponding to the infrared radiation. The thermal properties of light source with alternating modulation has been studied and verified based on the proposed electro-thermal modelling and compared to the measurement of the output signal of infrared sensor for different modulation frequencies and gas concentrations. A practical model for the description of relationship between gas concentration is realized and thermal parameters of light source are extracted. The measurement results show a great agreement with the simulation for behavior of signal. It also gives a new approach to build a theoretical model for all the NDIR measuring techniques.