The electronic structure of Ti alloys has been calculated by the recursion method. Alloying elements Ni, Co, Pt, Ru and Ir were confirmed to segregate on the surface of Ti alloys. Ni and Co atoms form atomic clusters, while Pt, Ru and Ir atoms form the ordered phase with Ti atoms. The microcells are formed between the area with alloying atomic clusters and the region without alloying elements. Ti is dissolved preferentially in the corrosive media, and the enrichment layer on the surface of Ti alloys is formed by the remaining insoluble grain of the alloying elements. The enrichment layer of alloying atoms serves as the electrocatalytic surface, which facilitates the passivation of Ti alloys and improves the corrosion resistance. The co-added alloy elements, such as Ru-Ni, Ru-Ir, Ru-Mo and Ru-W, have the same effect as adding the noble metals （such as Pt）.