PAL (Panoramic Annular Lens) was a hemispheric panoramic imaging system based on the principle of FCP(Plat Cylinder Perspective),field range of 360° around the optical axis could be imaged into a annular plane without any kinds of rotatable parts. The image was distorted,thus it was necessary to correct the deviation. An algorithm of correcting the image of a two-dimensional plane was provided based on the principle of FCP,after being treated by radical and tangential linear processes,image of the plane could be corrected into its former shape.