Ammonia （NH₃） is a representative carbon-free fuel， with its primary combustion products being water and nitrogen gas. Due to its unique advantage of zero carbon emissions， high proportions of ammonia co-firing strategy have been successfully implemented in decarbonization of thermal power boilers， internal combustion engines， and industrial furnace. As flame temperature is closely related to combustion efficiency and pollutant generation， it necessitates precise measurements for active control of low-pollution combustion processes. This paper presented the development of a measurement system based on mid-infrared tomographic absorption spectroscopy. By comprehensive analysis of absorption lines， we optimized the selection of absorption lines and finally selected the transitions near 2 482 nm within the fundamental band （v₃） of H₂O. By employing the multiple Voigt profile function， we achieved accurate fitting of the overlapping absorption features of H₂O spectra. Combining Abel inversion and regularization techniques， we realized calibration-free and quantitative measurements of flame temperature under different proportions of ammonia blending. The experimental results indicate that the flame sheet positions are located between 0.5 and 2 mm above the burner for pure ammonia flame and methane/ammonia co-fire flame. As the proportion of ammonia increases from 20% to 100%， the flame sheet gradually moves away from the burner， while the maximum flame temperature rises from approximately 1 600 K to 2 000 K. The proposed measurement technique and system developed in this study not only capture the non-uniform temperature distribution of laminar premixed flames along the axial and radial directions but also discern subtle differences in flame temperature under various combustion conditions. This system is particularly suitable for measuring the flame temperature of zero-carbon ammonia fuels.