A Bordoni type apparatus was used to measure the relative changes of the apparent Young's modulus and elastic strain of a sustained displacement specimen during aging at room temperature after charging with hydrogen or artificial partial stress relaxation. The Young's modulus was gradully increasing and the elastic strain decreasing during aging after artificial partial stress relaxation. However, the situation was just opposite during aging after charging, i.e., the Young's modulus was gradually decreasing and the elastic strain increasing. It has been proved that the presence of nickel hydride brings about the increase of the Young's modulus of pure nickel due to the change of chemical bond. The decomposition of hydride and escaping of hydrogen atoms from the specimen during aging after charging cause the decrease of the Young's modulus of nickel.