A three-dimensional lignin porous carbon/zinc oxide composite material and its preparation and application in the field of photocatalysis are disclosed. The method includes preparing a lignin/zinc oxide precursor composite by a hydrothermal method from a zinc salt, a weak alkali salt and an industrial lignin, and preparing a three-dimensional lignin porous carbon/zinc oxide composite material by high temperature calcination of the lignin/zinc oxide precursor composite. The composite material has a regular three-dimensional pore structure, with zinc oxide nanoparticles uniformly embedded among the three-dimensional lignin porous carbon nanosheets. Application of the composite material to the field of photocatalysis, especially as a photocatalyst for photocatalytic degradation of organic dye pollutants, can significantly improve the degradation efficiency and rate, and has potential application value in the field of photocatalytic degradation of organic pollutants.