Based on the formation and attenuation mechanisms of Fiber Bragg Gratings (FBGs),a model describing its attenuation law was established to study the effect of environmental temperature on its service life. This model discusses physical mechanisms of formation and change of the refractive index modulation,gives the relation of peak reflectivity between temperature and time. By experiment and numerical simulation,the rationality of theoretical model is verified. It is concluded that FBGs can work reliably for a long time under conventional conditions without consideration effects of other environment impacts except the temperature.