The rules of the influence of Cr ions with different valence on the formation and the crystal structure of ettringite were investigated by means of X ray diffraction and X ray photoelectron spectroscopy analysis test. The results show that the Cr3+ions slightly influence the formation inhibition of ettringite, and its crystallization is extremely small on the early hydration phase, while it is formed greatly on the later hydration phase, and the crystallization become thick and big, and the ratio of length to diameter of the crystal becomes smaller along with the development of hydration. While Cr6+ions show a positive effect on the formation of ettringite at the early hydration stages, and the crystallization is well. There is no significant change on the crystalline form along with the development of hydration. When the SO2-4 content is plentiful on the hydration liquid phase, both Cr3+ions and Cr6+ions can form chromite ettringite through lattice ion substitution, and Cr3+ions have a larger influence on the crystal structure of ettringite than Cr6+, and Al and S atomic binding energy of ettringite shows a significant decrease. The combination energy and quantity of Cr3+ ions on ettringite are higher than that of Cr6+ions.