Accurate and real-time diagnostics of combustion process is critical to understand combustion mechanism, improve combustion efficiency and reduce the production of pollutants. The thermometry of tunable diode laser absorption spectroscopy (TDLAS) technique is briefly introduced. Two adjacent water lines near 1397.75 nm are selected, and the TDLAS measurement system is established by using a multifunctional data acquisition (DAQ) card for signal processing and diode laser control. The measurements are performed on the instantaneous supersonic flow, the measure repetition frequency is 1 kHz, and the temperature of the evolution of supersonic flow is acquired.