Aimed at the problems of feature point solution of robot monocular vision calibration center target, projective change tangent invariability was used to establish the model of geometric solution of feature point of center target and to solve accurately. There were no modeling errors in the model in theory. In order to test precision and stability of geometric solution model, measure in three dimensional (3D) was carried out in part for center target feature points under the coordinate system of robot monocular vision calibration and for the plane grid target corner points. Experimental results show that the maximum relative error is less than 15% for the measuring length within 300 mm, and precision is quite high. The average absolute difference is all at about 02 mm for the distance between each point with no step jump, and the method is stable.