In this paper, a new type of lower limb powered exoskeleton is presented, which is based on a screw-nut actuated mechanism to help paraplegics to stand, walk and accomplish activities of daily living. The Denavit–Hartenberg method and the Kane method are adopted to establish a kinematic and dynamic model of novel lower limb powered exoskeleton to analyze the workspace and the control strategy simulation. A double-closed loop control strategy is proposed to ensure precision, and its effectiveness is validated. The results of prototype gait control and patient experiments show that the new type of lower limb powered exoskeleton can enable patients to realize stable and smooth walking.