Abstract: Two simple and efficient algorithms of sub-pixel corner detection for camera calibration dy using plane pattern were presented.The pixel level corners were detected by classical Harris corner detector,and then some methods were used to get sub-pixel accuracy.In one algorithm,the subpixel location was achieved through a quadratic approximation of the 3×3 neighborhood of the local maxima of the corner response function,and a closed form solution developed to the problem.In the other algorithm,the sub-pixel accurate corner locator was obtained from the observation that any vector from true corner location to its neighborhood is orthogonal to the image gradient.So the sub-pixel location was calculated iteratively by minimizing an error function.The result of the camera calibration shows that high precision can be acquired by using the sub-pixel algorithms and the mean reprojection error is below 0.15 pixels.