A high pressure and temperature fiber grating sensor was presented. The sensor was implemented by using three metal tubes. The central elastic metal tube was used to convert pressure into longitudinal strain. The outer tube was only affected by temperature. Fiber grating was fixed on both end of central and outer tube, so as to sense the wavelength increment introduced by the pressure. Temperature compensation scheme was studied, and two fiber Bragg gratings (FBGs) (pressure sensing grating and temperature sensing grating) with similar temperature coefficient were designed. High pressure and high temperature/humidity storage tests were carried out. Results showed that the sensor during the condition of 0～50 MPa had a pressure sensitivity up to 31.7 pm/MPa. After storage of 16 hours under 200 ℃ and immersion into 100 ℃ water for 6 hours, the fiber grating wavelength showed no obviously decay.