In order to calculate the parameters of the camera correctly, we must figure out the accurate coordinates of the certain
points in the image plane. Corners are the important features in the 2D images. Generally speaking, they are the points
that have high curvature and lie in the junction of different brightness regions of images. So corners detection has already
widely used in many fields. In this paper we use the pinhole camera model and SUSAN corner detection algorithm to
calibrate the camera. When using the SUSAN corner detection algorithm, we propose an approach to retrieve the gray
difference threshold, adaptively. That makes it possible to pick up the right chessboard inner comers in all kinds of
gray contrast. The experiment result based on this method was proved to be feasible.