Al and Y modified aluminide coatings were prepared by pack cementation process at 1000℃ for 2 h. The microstructure and constituent phases of the co-deposition coatings were studied, the formative mechanism and erosion behavior of the coating were also analysed. The results show that the coating prepared by co-depositing Al-Ce-Y at 1000℃ for 2 h have a multiple layer structure: an outer layer composed of NiAl and a little Al3Ni2 , a middle layer composed of Al3Ni2 and a Al-rich inter-diffusion zone. Y and Ce mainly existed in the outer layer, which plays the role of reducing the grain size and promoting permeation. The solid particle erosion resistance of DZ125 alloy with Al-Ce-Y coating was significantly increased at the small impact angle, and then the erosion rate of Al-Ce-Y coatings increased with the increasing of impact angles, and the erosion mechanism shift from plough and cutting damage to brittle fracture and fatigue failure. The erosion rate of Al-Ce-Y coating is higher than that of DZ125 matrix when the impact angle at 90°.