In this paper, we propose an accurate automatic chessboard corner detecting algorithm of sub-pixel precision. The algorithm is based on a novel hyperbolic tangent model. A set of corners are detected initially by Harris’ algorithm. Then the hyperbolic tangent model for each corner point is optimized by parameter adjustment. Finally, we use the optimal model to obtain the sub-pixel position of each corner with fake corner elimination. Experiments on three datasets show that the proposed method achieves a detection rate of at least 98% and a reprojection error in camera calibration of at most 0.85 pixels. Our algorithm significantly outperforms the methods in three related works.