A fiber optic temperature sensor based on extrinsic Fabry-Perot (F-P) cavity interferometric/intensity modulation mechanism is described. The light from a light-emitting diode (LED) is coupled into a 2×2 multimode fiber coupler C1 and propagates to the F-P sensor head. The light reflected from the F-P cavity is recoupled into C1, and then through another fiber coupler C2 the light is divided into two beams. One propagates to optoelectronic detector D1 and another through narrow filter propagates to detector D2. The two signals are transported to the computer through the optoelectronic conversion and amplifier circuit. A theoretical model for the temperature calculation and self-compensation has been worked out, which gives out the compensated intensity expression on the F-P cavity length, spectral width of the light source and band pass filter. The temperature calibration curve was obtained by fitting the experiment data to the theoretical model with Levenberg-Marquardt algorithm. A minimum temperature resolution of 0.1℃ and long term accuracy of ±0.2℃ were obtained over a temperature measurement range of 20～200℃.