Abstract: In order to identify the change of mechanical properties along the wall thickness of long-years-served boiler tubes, a group of 3-parameter data including micro area hardness, indentation remaining depth and plastic work along the wall thickness of a finishing superheater tube which had serviced for 105 h, were obtained by depth-sensing indentation (DSI) testing technology. Then by introducing M Dao’s method, the yield strength of certain area was deduced. So the strength change trend along the tube wall thickness could be revealed quantitatively.