To further investigate the application of group III nitride materials in optoelectronics, the phase stability, electronic structure, and optical and thermodynamic properties of GaBN2, Ga3BN4, and GaB3N4 using first -principles calculations with a quasi-harmonic approximation. These three nitrides have similar electronic structures (including band structures and density of states). With bandgaps of 3.129 eV, 2.315 eV, and 3.697 eV, these nitrides can be considered as direct bandgap semiconductors. GaBN2 is optically anisotropic, implying that it can be employed for UV shielding in optical systems. Furthermore, by studying the phonon properties of these nitrides to explore their thermodynamic properties, it was found that these materials are all dynamically stable.