12Cr steels have been applied on the turbine bucket and nozzle partition materials for the ultra super critical (USC) coal-fired power plant. Turbine bucket and nozzle materials are damaged by the solid particles within USC steam conditions. Therefore, they have been protected by the surface treatments such as ion nitriding, boriding and chrome carbide high velocity oxygen fuel (HVOF) spray coating. In this study, the surface treatment effects on the solid particle erosion (SPE) characteristic of 12Cr steels were examined in the temperature range of 540 to 620°C and the mechanisms of surface damage are investigated. The SPE of 12Cr steel originated from micro cutting, whereas, that of boriding and chrome carbide HVOF spray originated from the repeated collision, crack initiation and propagation. In case of 12Cr bare steel, the erosion of soft materials occurred in the impact angle range of 30° to 60° at test temperatures. The SPE resistances of boride and HVOF treated steels in the impact angle range of 30° to 60° at 593°C and 621°C were much higher than those of 12Cr bare steel.