The elastic constants of the interface of Nb-Si-N nano-composite film have been calculated with first principle method based on density functional theory ( DFT) . Two kinds of interfaces, namely the interstitial interface and the substitution interface, were under our studies. The bulk modulus of the interstitial interface and the substitution interface structure is 233 . 595 GPa and 280 . 204 GPa, respectively. Their shear modulus is 70 . 716 GPa and 125 . 677 GPa, respectively. Their Young’s modulus is 192 . 702 GPa and 327 . 994 GPa, respectively. Clearly, the shear resistant and the compress resistant of the substitution interface structure are relative better than those of the interstitial interface structure. Additionally, analyzing their Young’s modulus in all direction shows that the two interface structure is isotropic and the NbN structure presents anisotropic.