The CLAM steel(China Low Activation Martensitic steel)has been developed in China for use in advanced nuclear energy systems as structural materials.The heavy ions irradiation experiment was carry out to examine its radiation properties by measuring the dependences of radiation damage on irradiation dose up to 90 dpa at room temperature and on irradiation temperature up to 800℃at 15 dpa.The size of vacancy clus- The CLAM steel (China Low Activation Martensitic steel) has been developed in China for use in advanced nuclear energy systems as structural materials. The heavy ions experiment experiment was carry to to examine its radiation properties by measuring the dependences of radiation damage on irradiation dose up to 90 dpa at room temperature and on irradiation temperature up to 800 ° C at 15 dpa. size of vacancy clus-