The invention discloses a preparation method of polyimide composite coating. The method includes the following steps: step 1: preparing the polyimide spraying raw material, wherein the polyimide spraying raw material is thermosetting polyimide composite precursor slurry, thermoplastic polyimide composite precursor slurry or thermoplastic polyimide composite powder; step 2: performing surface oil-removing of the matrix and coarsening processing; and step 3: sending the spraying raw material prepared by step 1 to a thermal spraying flame flow, and spraying on the treated matrix surface to form the polyimide composite coating. The invention discloses the preparation method of polyimide composite coating, and the method has simple technology, high efficiency and low cost, and is suitable for site operation. The spraying is not limited by the size and shape of the workpiece. The prepared polyimide composite coating is combined well with the matrix, has effective antifouling and anticorrosion performances, and can be used for a plurality of antifouling and anticorrosion occasions such as external surface of industrial component used for ocean.