To study the behavior of hydrogen corrosion on U-2.5%Nb alloy (mass fraction), a gas-solid reaction system with an in-situ microscope was designed. The nucleation and growth of hydride of U-2.5%Nb alloy were observed continuously and recorded by the system. The results show that the growth velocity of hydride can be well characterized by the in-situ microscope. The growth kinetics result indicates that the relation between growth velocity of hydride and time is linear. Hydride front velocity increases with the increasing temperature, which follows the Arrhenius law at about 125 oC. The reaction activation energy is 24.34 kJ/mol. But at high temperature (>125 oC), the growth velocity decreases sharply with the increasing temperature