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The selective catalytic reduction and non-selective catalytic reduction (SCR/SNCR) are the most popular de-NOx processes for coal-fired power plant, where the real-time temperature is a significant parameter. A new developed tunable diode laser spectroscopy used for measuring the temperature of ammonia (NH3) in the process of SCR/SNCR influenced by strong exhaust gas matrices CO2 and H2O was presented in this paper. Two lines near 6605 cm−1 were selected, with rather weak temperature dependency and minimal interface from CO2 and H2O according to HITRAN12 database. A homemade heating equipment for high temperature laser spectroscopy measurement was developed based on an ARM microcontroller. The temperature calibration experiments of absorption lines were carried out at variable concentrations under different temperatures. The spectral signals of 2.5%, 3.5% and 4.5% NH3 were observed for validation of the generalization and robustness of the sensor. The calibration and validation experimental results show that the maximum measurement error and global average error of the temperature sensor with the temperature ranging from 453 to 653 K are less than 2% and 1.38%, respectively. It demonstrates that our proposed sensor with high accuracy and linearity, and can be utilized to measure the temperature in SNCR/SCR process. [ABSTRACT FROM AUTHOR]