Based on the temperature measurement technology of tunable diode laser ab-sorption spectroscopy, the simulation and experimental research on the temperature measurement of CO2 gas emitted by D4114B Diesel engine is realized. The light source model, gas chamber model and data detection model were established by using SIMULINK, which is more general numerical simulation tool in MATLAB. Under the simulated Diesel engine emission environment, the measured CO2 gas temperature was obtained by model simulation and analyzed. The simulation relative error was 0.077%. The marine D4114B Diesel engine was used as the test object, the visual window was reconstructed on the exhaust light path, and an optical path test system was established. The tunable diode laser was used as the detection light source to carry out on-line test research on the CO2 gas temperature in the exhaust gas emission. The relative error was 4.4%. The results show that the model built by SIMULINK can reflect the actual laser modulation effect and CO2 gas absorption. The simulation results have certain reference value for the research of tunable diode laser absorption spectroscopy temperature measurement system.