The formation of two-dimensional (2D) ultrathin films in III-nitride compound on Ag(111) substrate is investigated using density functional calculations. The calculations demonstrate that there is faint charge distribution between III-nitrides with 2D hexagonal structure and Ag(111) substrate while metallic bonds are formed at the interface for III-nitrides with wurtzite structure. This indicates that the lattice constraint of Ag (111) substrate is negligible for III-nitride compound ultrathin films with hexagonal structure. Furthermore, the hexagonal structure is more stable than wurtzite phase for the films up to 15 monolayers due to interlayer electrostatic interactions. The results suggests that various 2D III-nitride compound ultrathin films can be formed on Ag(111) substrate.