A method for determining camera intrinsic parameters is presented.First,the images of the two circular points are derived from the images of a single rectangle in space.The acquired images contain the parameter r,the ratio of the lengths of two adjacent sides of the rectangle.Then according to the constraints of the circular points on the camera intrinsic parameters,a group of nonlinear equations are contructed.By solving a positive root of a polynomial equation with degree three,the nonlinear constraints are turned into linear constraints determine the camera intrinsic parameters.In addition,the necessary and sufficient condition for the constraint system with a unique solution is also provided.Experimental results show the high accuracy of the approach.