In this paper we describe the use of a genetic algorithm and two thermally-modulated fiber Bragg grating's (FBG's) reflection intensity spectra for inversely extracting complete physical parameters. The fiber Bragg grating’s complete parameters included the grating period, grating position, grating length, chirped direction, and refractive index modulation. In this study, a uniform and chirped fiber Bragg gratings are synthesized successfully in the numerical analysis. Also, the experimental results show that the complete parameter synthesis in grating period, grating length, refractive index modulation and various grating positions from a 10 mm length uniform FBG have been recovered accurately. After finding those physical parameters, the arbitrary distributed strain sensing technique is easy to accomplish by using two fiber Bragg gratings sensing techniques.