This invention relates to a method for preparing polyimide thin film containing chromophore. The polyimide thin film, prepared by vapor deposition polymerization, can retain good thermal stability and chemical stability as that prepared by traditional method, and has such advantages as high uniformity, high compactness, no pin holes, no need for catalyst, no residual solvent, high purity and simple process. The polyimide thin film is suitable for fabricating photoelectrical devices such as optical switch.