Cavitation and slurry erosion are two major damages to the overflowing components of hydraulic machinery including hydro turbine, which can reduce its service life. Depositing coating on the surface of substrate materials of overflowing components by using specific techniques to improve the erosion resistance has aroused increasing concern. The common metal materials of hydro turbine and the research progress concerning hydro turbine materials as well as corresponding cavitation and erosion failure mechanism by domestic and overseas researchers were reviewed in this paper. The cavitation and slurry erosion resistance of coatings prepared by untilizing high velocity oxy fuel spray (HVOF), laser cladding, physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods adopted in domestic and overseas published literatures were mainly discussed. In accordance with material properties, the surface strengthening materials in the literatures were categorized into alloy materials, ceramic materials, composite materials, metallic glass materials and diamond like materials. The failure mechanisms of various coatings were analyzed by combining with the coating preparation process. Effects of micirodefects in the coatings such as pores, cracks, unmelted particles, hardness, bonding strength between substrate and coating, thickness on erosion resistance were discussed based on cases. Finally, expectations about manufacturing technology and materials were proposed in respect of current research and application status. It is pointed out that the effective way to resolve the combined cavitation and slurry erosion under the complex multi phase flow conditions is preparing efficient coatings by making use of advanced coating technologies and new coating materials.