Abstract: The fretting wear behavior of Inconel600 alloy for steam generator heat exchange tubes at different displacement amplitudes was investigated with a SRV IV fretting tester. The effects of displacement amplitude on the friction coefficient and wear volume were analyzed. The worn surface and subsurface morphology were observed by optical microscopy and scanning electron microscopy, and the tribological transformed structure was observed by transmission electron microscopy. It was found that the friction coefficient and wear volume increased with the displacement amplitude, and the fretting wear mode gradually transformed from mainly adhesion of the partial slip regime to absolutely slide of the gross slip regime. The wear mechanism correspondingly gradually changed from adhesive wear to a combination of oxidation and delamination wear. Microcracks were observed at the junction of the adhesion zone and the slide zone and in the whole slide zone of the wear scar. The oxygen distribution density in the adhesion area was almost the similar as the matrix located outside the wear scar, and oxidation mainly occurred in the sliding zone. Severe plastic deformation appeared just under the wear scar, resulting in its nanolization. The grain size in the tribological transformed structure layer was about 100nm, much smaller than 15 to 30 μm of the original grain size.