It is well known that human body can be approximately modeled by articulated object.The anatomical knowledge reveals that there exist multiple constraints on human motion such as rigidity constraint

static rotation constraint

and so on.In this paper

we estimate 3D human motion by rigidity and coplanar constraints.In theory

we analyze the 3D structure of multi-link from motion

and investigate the relationship among the number of the frames and links and the number of equations and unknowns.By Genetic Algorithm

the robust numerical solutions can be achieved.The experiments with the simulated data and the real images are included to demonstrate the validity of the theoretic results.