ing at the problem of distortion of the panoramic image collected by the conical catadioptric panoramic imaging system, a panoramic image expansion method of inner surface of cylindrical objects under the conical bidirectional projection model is proposed. Forward and reverse projection models with distortion parameters are established, first, the pixels of the panoramic image of cylindrical inner wall are reversely mapped to the expanded image, and then forward the missing pixels in the expanded image to the original panoramic image, through the panoramic image and the expanded image corresponding to the coordinate mapping relationship of the pixels, the expansion of the panoramic image of cylindrical inner wall is realized. The experimental results show that the tangential and radial distortion of the panoramic image of cylindrical inner wall are corrected better, the positioning accuracy of the bidirectional projection model of the cone surface is sub-pixel level, comparing with the approximate expansion method of concentric rings, the information entropy and the average gradient are both improved to different extents, it can be effectively applied to the expansion of panoramic images of cylindrical inner wall.