The kinematical equation of man-machine exoskeletons is established based on differential geometry homogeneous coordinates equation,according to the lower limb motion parameters,the boundary conditions are got,and then the motion trajectory of ankle is drawn by using the Matlab. In the face of the human lower limb exoskeleton and lower limb movement in the presence of interference problems,the equations of shortest distance of noncoplanar lines are established,and the equations are solved according to the condition that the shortest distance between lower limb exoskeleton thigh and human thigh is greater than the human thigh muscle,the relation of the distance of rotary axial between human lower limbs and lower limb exoskeleton is obtained. Based on the theory above,the design of multi-joint and low-resistance lower limb exoskeletons is finished.