If a long-period grating is written in the hydrogen-loaded standard SM fiber, using the amplitude mask, the thermal stability will be decreased because of the presence of H 2, which makes it difficulty to fabricate an ideal long-period fiber grating (LPFG). It is pointed out both in aspects of theory and experiment that if the solubility of H 2 in the hydrogen-loaded fiber is lowered and using the technique of uniform UV exposure properly, the thermal stability of LPFG could be improved greatly.