A new type of pressure and temperature fiber Bragg grating(FBG) sensor used in oil wells is presented. The FBG sensing principle of detecting pressure and temperature is analyzed. On this basis, a sensor is designed to measure the parameters of pressure and temperature in oil wells. From the temperature and pressure test, the relationship between the pressure/temperature and the central wavelength of FBG is obtained, and the analytic expression of pressure-response sensitivity is found. The sensor can measure pressure and temperature at the same time. The experimental results show that the temperature sensitivity is 1.6357×10^－5/℃ when the temperature ranges from 10℃ to 100℃, and the pressure sensitivity reaches to 1.245×10^－4/MPa when the pressure ranges from 0 to 20 MPa. The sensor can meet the application in oil wells.