The invention provides a two-dimensional layered ternary nano-composite photocatalyst, and a preparation method and application thereof. The preparation method comprises the following steps: placing 
melamine in a 
muffle furnace, and calcining to obtain g-C3N4; 
grinding the g-C3N4 into 
powder, adding the 
powder into deionized water, and performing 
ultrasonic dispersion to obtain a g-C3N4 suspension; and adding 
nickel nitrate hexahydrate and 
cobalt nitrate hexahydrate into the g-C3N4 suspension, stirring for a first time, dropwise adding 
ammonia water, transferring into a high-pressure kettle, carrying out a 
hydrothermal reaction, and carrying out post-treatment to obtain the two-dimensional layered ternary nano-composite photocatalyst. A water reduction cocatalyst and a water oxidation cocatalyst are introduced at the same time, under the synergistic effect of the water reduction cocatalyst and the water oxidation cocatalyst, 
electron-hole separation is accelerated, and the 
catalytic efficiency is improved; and the material with a two-dimensional 
layered structure is compounded, so that the interface contact area is increased, the transfer of interface charges is accelerated, and the photocatalytic activity is effectively improved.