In his article, we explore a method for measuring position and attitude parameters of protable three-coordinate equipment based on monocular vision. The T-Probe of Laica is used as the experiment equipment and its four coplanar LEDs are chosen as feature points. While measuring, the probe contacts the measured point, the CCD camera takes the image of four coplanar feature points, the image coordinate of the feature points are accurately obtained by image processing programs. Using the linear idea for solving the P4P question, the coordinate of these feature points and attitude of object are gotten. Eventually, the measured points' coordinates are derived.