Abstract: Due to the characteristics of a lens, images grabbed from the endoscope have significant “barrel” distortion It is necessary to correct the distortion in the application of endoscope Asari and Chao Zhang proposed distortion correction techniques, which are based on the least square method But they do not take the distortion center as an adjustable parameter However the estimation of distortion center is not accurate enough and this will have an important effect on the distortion correction In this paper the Chao Zhang’s technology is modified The distortion center is taken as an adjustable parameter Optimization procedure is used to calculate a more accurate distortion parameter Experiment shows that the new method can get a much better distortion result