Abstract: Based on kinematic analysis method in robotics，three kinds of variational geometric constraints （VGCs） are specified based on the feature classification in ISO/TC 213，and the concept of variational geometric constraints network（VGCN） is defined．Kinematic model of VGCN is studied based on screw parameters，and the general expressions of the model are presented．Finally，application of the model to computer aided tolerancing is discussed．An example is analyzed to show the effectiveness of the proposed scheme．