Abstract: The Charpy impact specimen and 0.5T-CT specimen extracted from a certain domestic RPV material are irradiated in HFETR with fast neutron（E＞1 Me V）influence of 3.0×10¹⁹ cm^-2. In accordance with unirradiated and irradiated Charpy impact test, the measured ΔRT_NDT is 48℃, while, according to the fracture toughness test in ductile-brittle transition region, the measured ΔT₀ is 53℃, these actual measurement results demonstrate that the irradiation embrittlement effect is obvious. The RT_T0 based on the fracture mechanics methodology to be an alternative indexing to RTNDT could further exploit the underlying safety margin of RPV and improve the economy of NPP.