It is well known that vanadium alloy will face to strong neutron irradiation and hydrogen environments as a structural material in a fusion reactor. Some researches have reported that vanadium alloy took strongly hardening after an exposure to hydrogen environment and irradiation by neutron at a temperature lower than 400℃. The ductility of the alloy was lost largely, even entirely brittle fracture occurred sometimes in tension loading of the alloy. Therefore, it's to get the knowledge of the hardening mechanism and the fracture mechanical for the purpose to improve the performances of the alloy under the circumstances.