In the paper we show that based on coplanar constraint, the motion and structure of the articulated object can be determined within a scale factor from a monocular sequence of images. By Genetic Algorithm, we achieve the unique robust numerical solution to motion estimation of the coplanar links. Then we apply the techniques to human motion analysis, and obtain the 3D motion data of joints, reanimate successfully the data. The experiments with simulated data and real images are included to demonstrate the validity of the theoretic results.