Tunable diode laser absorption spectroscopy (TDLAS) has been widely used in combustion diagnosis because of its excellent characteristics such as fast response, high sensitivity and non-intrusive feature. The system uses a pair of H2O absorption lines (1395.51 nm and 1395.69 nm) by a narrow linewidth and tunable wavelength distributed feedback (DFB) laser. The laser is divided into four beams by a 1×4 optical fiber splitter to measure the temperature and H2O concentration simultaneously. Sectional measurement is proposed to improve the temperature accuracy from 10% to 3% compared with K-type thermocouple. What′s more, the temperature and H2O concentration at combustion center position are measured while the ratio of air and fuel changes. The results show that combustion temperature of central area at the three kinds of combustion state has difference of about 80 K, and the H2O concentration change is well consistent with temperature change, demonstrating the stability and feasibility of the experimental setup and the data processing method. This provides strong support for tomographic diagnosis and optimization of combustion efficiency of coal-fired boiler in the future.