Abstract: The small punch test method was suggested to measure the strength after irradiation using the load after irradiation and the relation between the load and the strength before irradiation. The strength after irradiation of the domestic A508-3 steel was measured using this method. The small punch test result indicates that the strength of the domestic A508-3 steel becomes bigger after irradiation. The sample was observed and the fracture pattern was determined by means of scanning electron microscope. The differences of the sample surface topography before and after irradiation explain the reason of the irradiation hardening phenomenon. Finally, the accuracy of the measurement was discussed and the improving advice was given.