Long Period Fiber Gratings(LPFGs) were inscribed by using a 800 nm femtosecond laser and their high-temperature properties were verified in this paper. Firstly, an inscription system for the laser into fiber cores was designed using a camera and an electric moving platform. With controlling a pulse laser of 1.3 mW, a LPFG was inscribed in a non-hydrogen-loaded bare fiber using point by point technique, and the resonant peak of the LPFG is about -17 dB in the 1 200~1 700 nm band. Then, high temperature sensing experiments were performed on the LPFG by a high temperature box, obtained results show that the linearity of the resonance peak changes is about 0.992 and temperature sensitivity is 0.056 nm/℃ at 300-800 ℃. It demonstrates that the inscription technology for LPFGs by using the 800 nm femtosecond laser is feasible and obtained LPFGs have good response characteristics and stability, and are suitable for the high-temperature measurement.