The invention discloses a novel graphite phase carbon nitride polymer material, a preparation method and applications thereof, and belongs to the technical field of functional materials, wherein the carbon nitride material has a layered structure, has good crystallinity, and has a chemical formula of g-C3N3, and the polymer material can be peeled into a single-layer or few-layer two-dimensional material through a chemical or mechanical method. The preparation method of the graphite phase carbon nitride polymer comprises: under inert gas protection or air, using an appropriate amount of a monomer as a reactant, cutting to obtain a metal sheet with an appropriate size, ultrasonically cleaning with water and an organic solvent, drying, adding to a reactor, properly placing the metal sheet, heating to a temperature of 180-300 DEG C, maintaining for not more than 48 h, and cooling, wherein the sheet-like material loaded on the surface of the metal sheet is the CN polymer. According to the present invention, the preparation method has advantages of simple steps, high yield and cheap raw materials; and the obtained material can be used for a variety of purposes such as electrocatalytic hydrogen evolution, photocatalytic hydrogen evolution, water production and oxygen production through photolysis of water, decomposition of pollutants, and the like.