In view of the application of gamma-AlON as transparent structural materials, it is significant to have a deep understanding of mechanical properties of gamma-AlON as well as their response to external pressure. First-principles calculation combined with bond valence models was used to reconstruct Fd3m structure, and explore the composition and applied pressure dependence of mechanical properties of Al24-8/3xO24+8xN8-8x. The reconstructed Fd3m structure of Al24-8/3xO24+8xN8-8x was proved to be reasonable. The investigation demonstrated that the hardness and bulk modulus of bonds can be enhanced by increasing the ratio of bond valence to bond length and the bonds in octahedra contribute more to hardness and bulk modulus of Al24-8/3xO24+8xN8-8x. The applicability of the inferences was assessed by MgAl2O4 and c-Si3N4. It can be inferred that the inferences cannot be applied to other spinel-type compounds but also provide guidance to designing new spinel-type compounds with desirable hardness and bulk modulus.