The invention discloses a method for preparing a titanium nitride-based composite material, and belongs to the technical field of preparation of inorganic non-metal nanometer materials. According to the preparation method, a titanium nitride substrate is subjected to controllable oxidization by adopting a gas phase hydrothermal measure, and titanium dioxide is grown in situ on the surface of the substrate to obtain the titanium nitride-based composite material. By controlling a preparation process, composite materials with different two-phase proportions can be obtained; the preparation method is a simple and efficient composite synthesis method; particularly, the composite material prepared by the method has high interface contact, effective transmission of charge carriers between two phases is ensured, and the problem that high-temperature calcining is required in the conventional compound method is solved at the same time.