Designing flexible and efficient lower extremity exoskeleton is one of the key technologies to improve weight based lower extremity exoskeleton, the man machine cooperation as well as the bearing capacity. This paper presents an adaptive characteristic structure with lower extremity exoskeleton form of mechanical structures. This structure can change itself according to the constraint caused by the wearer's gait. The degree of freedom of the form also will be changed, thereby it will change the spatial force of the closed loop lower extremity exoskeleton. Finally we analysis the human lower extremity movement space via simmechanics and compare it with the normal person. The conclusions can provide supports and verify the feasibility of this structure.