Abstract: To explore the effect of hydrogen-loading on B-Ge co-doped fiber chemical composition grating (CCG), the thermal stability and generating property of B-Ge co-doped fiber CCG caused by hydrogen-loading have been experimentally studied. Different dopant concentrations of two fibers have been used as the subjects for comparison, one is w(Ge)=9.640% with w(B)=0.475% and the other is w(Ge)=28.277% with w(B)=2.375%. The result shows that, with the same conditions of hydrogen-loading and high temperature, the higher concentration of germanium in the fiber is, the easier to bring about the decay of fiber Bragg grating (FBG) and the thermal instability of CCG is. For the same fibers with different hydrogen-loading conditions, hydrogen would increase the reflectance of grating, but make its stability worse. By trial, the excellent thermal sensor with better stability in high temperature condition is fabricated, which can be used in the range from 10~1 010 ℃ with reflectance of about 40%.