Rare earth has been widely used in materials manufacturing to improve hardness and toughness. In this paper, conventional, nanostructured and CeO2 modified WC-12Co powders were sprayed by using HVOF spraying technology. Erosion-corrosion behavior and interaction role of erosion and corrosion of the three coatings in 3.5wt% NaCl solution were investigated. In situ observation method was employed to analyze failure mechanism. The results showed that CeO2 modified WC-12Co coatings possessed the best erosion-corrosion resistance, which is the worst for the conventional WC-12Co coating. The addition of rare earth CeO2 into conventional WC-12Co coating can improve the erosion-corrosion behavior. Results suggested that the erosion-corrosion mechanism in the three coatings was dominated by corrosion-enhanced erosion. However, the extent of corrosion enhanced erosion was different.