Distributed temperature sensing up to 600°C at a fiber length of 100.75 m based on optical frequency domain reflectometry (OFDR) was demonstrated using a standard single-mode fiber (SMF) without any treatment. The spatial resolution was 2.5 mm. An algorithm, instantaneous optical frequency resampling (IOFR), to eliminate the nonlinearity of the laser source was proposed and used to obtain calibrated reference and measurement signals that were used for temperature demodulation. Moreover, the temperature response stability of the annealed SMF was better than that of un-annealed SMF, where the temperature sensitivity was 1.96 GHz/°C at 600°C.