Through the kinematic analysis approach of mechanism with closed loop vector equations, three kinds of link units, including link vector unit, Jacobian unit and Jacobian differentiation unit, were proposed. Since they are only relative to sizes and shapes of link, these units can be programmed with link drawing subprograms together. Using the effect factors, the units were combined together to build Jacobian matrix and differentiation Jacobian matrix of whole mechanism, and a new automated modeling approach to analyzing planar linkages motion was gotten. This paper also discussed general method analyzing closed loops in complex linkages, as well as algorithm for automated modeling and kinematic analysis. Programming the kinematic analysis and testing with many planar linkages showed that the approach is suitable for automated solving kinematics of complex mechanism due to its modular property. 