Point defect introduction is an important method for inducing robust unconventional magnetic behaviors. Here, we studied the effects of atomic vacancies, including Ga (V-Ga) andNvacancies (V-N), on the magnetic properties of two-dimensional (2D) planar and buckled GaN based on density functional theory (DFT). The results demonstrate that the introduction ofV(Ga)causes nonzero magnetic moments in 2D planar and buckled GaN, whileV(N)does not. Furthermore, for the planar structure, distinct magnetic behaviors occur in two different V(Ga)ratio regions. Notably, when theV(Ga)ratio is greater than 1/16 (1 Ga vacancy per 16 Ga atoms), 2D planar GaN exhibits a half-metallic nature, and its spin polarization at the Fermi level reaches 100%. Utilizing 2D planar GaN with highV(Ga)ratios as ferromagnetic layers, a magnetic tunnel junction with an ultra-high spin filtering effect at the Fermi level can be obtained. On the other hand, the planar structure with a low vacancy ratio (less than about 1/16) remains semiconductive. In this structure, we found that the band gap increases with decrease inV(Ga)ratio. As for 2D buckled GaN, it exhibits aV(Ga)-dependent nonzero band gap for anyV(Ga)ratio. In this case, the band gap can be tuned by varying theV(Ga)ratio.