This study experimentally investigates the effect of heat treatment on Rayleigh scattering based distributed single-mode fiber optic temperature measurement. A finite element model was established to investigate the effect of thermal expansion of coatings on the optical fiber core strains and thus, temperature sensitivity before the coatings soften and melt away. A theoretical derivation for the fiber core strains, using Lame equations, was performed to validate the accuracy of the finite element model. It was found that the one-time heat treatment eliminates the hysteresis effect and stabilizes the Rayleigh scattering based fiber optic temperature measurement up to 1000 °C. The typical dual-layer coating effect on the temperature sensitivity of the Rayleigh frequency shift can be neglected at high temperatures in civil engineering application. Numerical parametric studies are performed to design coatings of fiber optic temperature sensors. The present study is promoting distributed fiber optic temperature sensor development and application.