Abstract: The domestic A508-3 steel is a kind of low alloy ferritic steel, using for the reactor pressure vessel（RPV）.The material has significant ductile-brittle transition behavior, and after neutron irradiation, it resulting in significant irradiation embrittlement effect, reducing the material toughness, increasingthe risk of brittle fracture. To master the neutron irradiation effect on the fracture toughness of the pressure vessel steel, fracture toughness tests have been done by A508-3 0.5CT specimens, and the analyzed the neutron irradiation on A508-3 steel fracture toughness combining with the fracture data before and after neutron irradiation.