Abstract: The 7075 aluminum alloy flat against GCr15 steel ball were chosen as friction pair. The effect of water medium on the dual-rotary fretting (DRF) wear behavior of 7075 aluminum alloy has been investigated by using an advanced dual-rotary fretting rig. Base on the analysis of the frictional kinetics and the observation of wear morphologies, the damage characteristics of 7075 aluminum alloy in water medium were discussed in detail. The results indicate that the water medium had significant effects on the fretting running characteristics and the damage mechanism. The delamination phenomenon under water medium were more obviously in the partial slip regime and the mixed fretting regime than that of dry condition, and the fretting damage was accelerated in water medium. In slip regime, the main wear mechanisms were gradually changed into abrasive wear, a mixture of the debris and water can more effectively reduce the friction coefficient and mitigate the fretting damage than pure water. In addition, two linear relationship between accumulated dissipated energy and angular displacement amplitudes can be found in water medium and dry condition.