An accurate and efficient demodulation algorithm for a fiber Bragg grating (FBG) strain sensor has been proposed and demonstrated. An accurate demodulation can be achieved by scanning only the 0.15-nm reflection spectrum of the FBG sensor instead of scanning the complete reflection spectrum. The proposed algorithm was first used to calculate the integration of 15 regions (10 pm per region) to calculate the wavelength drift. This algorithm is good in that the demodulation time can be greatly reduced without degrading the demodulation accuracy. Hence, the efficient algorithm, which can support a short demodulation time of a low-cost demodulation system, is very suitable for high demodulation rate requirements of the high-speed sensing systems.