Based on the self-developed experimental apparatus, the wet steam erosion experiments were performed on polished steel specimens. Scanning Electronic Microscope (SEM) and Atomic Force Microscope (AFM) were used to identify the pit characteristics. The experimental results showed that there was little damage on the surface after being impacted by wet steam erosion. However, when the micro-particles were added into the wet steam, not only indentations and scratches but also craters appeared on the eroded surface. Some characteristics of crater, such as the circular shape and intergranular fractures, make the damages distinguish from those of the water-drop or micro-particle impact to solid wall, and they
are considered as the results of cavitation erosion.