Fiber Bragg gratings (FBGs) are inscribed in both H₂-loaded and H₂-free fiber using 800 nm femtosecond laser, 244 nm Ar⁺ laser and a phase mask. The regeneration of three kinds of FBGs is observed in different processing temperatures. The models of regeneration process as well as regeneration temperature versus time are established. The FBGs regeneration temperature thresholds are defined. Experimental results and model analysis show that the regeneration temperature thresholds of femtosecond FBG written in H₂-free fiber, femtosecond FBG written in H₂- free fiber and ultraviolet (UV) FBG in H₂- loaded fiber are around 888 ℃ , 780 ℃ and 770 ℃ , respectively. The regenerated FBGs in H₂-loaded fiber decay in case of high temperature, while regenerated femtosecond FBG in H₂-free fiber has well temperature stability.