This paper investigates the influence of SiC dosage on the high-temperature mechanical properties (compressive strength, flexural strength, and bond flexural strength) of geopolymer mortar. The findings reveal that appropriate amount of SiC was found to improve the high-temperature mechanical properties of geopolymer mortar. Compared to the specimen without SiC, the addition of 3 wt. % SiC to the geopolymer mortar resulted in a noteworthy 14.59% increase in compressive strength at 300 °C, along with respective augmentations of 24.72% and 22.54% in flexural strength and bond flexural strength at 200 °C. Utilizing the experimental data as a foundation, a thermodynamic mathematical model was formulated, linking the strength and temperature parameters of SiC-modified geopolymer mortar. Furthermore, FTIR (Raman and Fourier transform infrared) analysis indicated that the polycondensation reaction of geopolymer mortar treated at 300 °C was promoted, and the products of displacement reaction increased, which provides a plausible explanation for the observed enhancement in compressive strength at 300 °C. Consequently, it is found that the incorporation of SiC can enhance the high-temperature mechanical properties of geopolymer mortar.