This paper deals with the creep-fatigue defect growth behavior at the defect front of a high temperature cylindrical structure subjected to a cyclic axial tensile loading and a thermal loading in the LMR(Liquid Metal Reactor) structures. The defect growth evaluation was carried out per the France RCC-MR A16 guide and UK R5 code and their results were compared. The creepfatigue structural test to confirm the evaulated results was carried out with a induction heater. The defect front was investigated at every 100th cycle of a testing by using the metallurgical inspection technique with an optical microscope. From these results, we showed that the creep-fatigue defect behavior of a high temperature structure can be predicted with a conservatism by following the RCC-MR A16 guide and the R5 code.