Fiber Bragg gratings (FBGs) have been widely used in the modern sensing field, but the cross-sensitivity characteristics between temperature and strain greatly confine its application in optical fiber sensing system. In this paper, a demodulation scheme was proposed based on genetic algorithm. A fast demodulation model of genetic algorithm was established. According to the mathematical analysis, the genetic algorithm fitness function and target equation were determined. With the proposed scheme, the demodulation results for different center wavelengths and peak reflections of the two FBGs were discussed. Numerical results demonstrate that the proposed demodulation scheme based on genetic algorithm can effectively demodulate the change of the temperature and strain separately without the requirement of two same fiber grating in the method of the traditional reference fiber grating. The accuracy of temperature and strain measurement are 0.1 ℃ and 1.5 με, respectively. This scheme can make the construction of fiber sensing system easier.