Spinel type Aluminum oxynitride(γ-alon)solid solution exists in the Al2O3-rich region in Al2O3-AlN systems.The first-principles calculations facilitate our investigations on composition-dependence of structural,electronic,optical and mechanical properties in γ-alon without the limit of experimental solubility.The constant anion crystal structure of γ-alon was described as the solid solution of spinel phase γ-Al2O3 and the ideal Al3O3N with formula of Al(8+x)/3O4-xNx(0 ≤ x ≤1)in theoretical study.We constructed supercell model for γ-Al2O3,Al22O30N2,Al22.5O28.5N3.5,Al23O27N5,Al23.5O25.5N6.5 and Al3O3N corresponding to x = 0,0.25,0.44,0.63,0.81 and 1 to evaluate the lattice constant,bond orders,dielectric functions,bulk modulus,shear modulus,Poissons ratio,and hardness with high accuracy.Our results show that the crystal structure and properties could be tuned by composition of nitrogen.The unit cell expands with increasing Al3O3N composition.