Graphite, as an important carbon material, is widely used in several fields owing to its excellent thermal/electrical conductivity, robust chemical stability, abundant availability, and low cost. A lot of research works have demonstrated that graphite can be doped with heteroatoms to enhance the electrocatalytic activity of hydrogen evolution reactions (HER) and the oxygen evolution reaction (OER). In our work, N/P co-doped graphite nanosheets (NP-GP) were prepared by a high-temperature vapor-phase method using graphite powder, melamine, and NaH₂PO₂ as raw materials. NP-GP exhibits bifunctional electrocatalytic OER and HER activities with an overpotential of 314 mV at 10 mA/cm² in 1 M KOH and an overpotential of 69.4 mV at -10 mA cm^-2 in 0.5 M H₂SO₄ after two-step cyclic voltammetric (CV) activation. And at the same time it keeps good electrocatalytic stability. The impact mechanism of two-step CV activation on the active sites of electrocatalysts was deeply studied. This work provided a new idea for the subsequent design of heteroatom-doped carbon materials as highly efficient and economical multifunctional electrocatalysts.