Hexagonal boron nitride (h-BN) is the most well-known wide band gap two-dimensional (2D) material (> 6 eV). To achieve its applications in optoelectronic devices, the conductance of h-BN must be implemented to the extent that it can be fabricated into a p–n junction. Here, we demonstrate a method to improve the surface current of p-type h-BN monolayer by introducing additional nitrogen gas flow during growth. First-principles calculations were conducted to show that nitrogen atmosphere can promote the formation of boron vacancy, making a low barrier site for Mg doping incorporation. Magnesium-doped h-BN monolayer was achieved using a low pressure chemical vapor deposition method under N2 flux. The surface current has been enhanced by three times up to 16 μA under 4 V external voltage. This approach provides potential applications of controllable conductive h-BN film for two-dimensional optoelectronic devices.