Tunable Diode Laser Absorption Spectroscopy (TDLAS) technique has many significant advantages such as non-intrusive compared with traditional combustion parameter measurement techniques. In this paper, according to the absorption lines optimization criterions, the 7444.352+7444.371 cm-1 and 7185.597 cm-1 line pair of water vapor (H2O) is selected for the temperature measurement of combustion environment in 900-1600K region, and two most important influencing factors (temperature and pressure) are analyzed by simulation of absorption spectrum based on HITRAN. Therefore, TDLAS system using the 7444.352+7444.371 cm-1 and 7185.597 cm-1 line pair based on Time-Division-multiplexing (TDM) strategy has been designed. This TDLAS system has been applied for the temperature measurement in the exhaust of Rocket Based Combined Cycle (RBCC) engine. Compared with the pressure measured by the pressure transducer in combustion chamber, the tendency of temperature measurement has well agreement with the pressure. The result of temperature measurement using TDLAS technique has great importance to the evaluation of RBCC combustion efficiency.