High velocity oxygen fuel (HVOF) sprayed WC-Co coating has been widely used in the surface protection of components for excellent corrosion resistance and wear resistance. However, with the increasing deteriorated service environment, higher comprehensive properties of WC-Co coating are required. Addition of rare earth elements into WC-Co powder is expected to be an effective way. In this work, the micro WC-12Co, nano modified WC-12Co and CeO₂ modified WC-12Co coatings were prepared by HVOF on the Q345 steel substrate. The microstructure, corrosion morphology and phase structure of coatings were observed by SEM and XRD, and the micro-hardness is measured. The corrosion behavior of the coatings in 1 mol/L H₂SO₄ solution was investigated by polarization test and immersion corrosion test. The results show that the addition of nano-sized CeO₂ in the WC-12Co coating not only purifies the grain boundary and increases the micro hardness, but also significantly reduces the porosity of the coating, which can effectively decrease the occurrence of local corrosion. Meanwhile, the addition of nano CeO₂ can make the electrode potential of coatings shift positively, reduce the corrosion current density and passivation current density, and then improve the corrosion resistance of the coating. The corrosion mechanism of nano CeO₂ modified WC-12Co coating is local corrosion which induced by the pore. Co bonding phase at the pore is constantly being corroded, causing WC particles to lose the support function and to fall off, which promotes the corrosion of the coating, so that the pores are enlarged to form corrosion pits. For the micro WC-12Co coating and nano modified WC-12Co coating, not only the outermost layer of the Co bonding phase is corroded, but also serious local corrosion occurred in the pores.