In the past decades, lots of wearable lower limb exoskeletons have been developed with the aim of augmenting or assisting motion activities in daily life. In this paper, the design of a wearable lower limb exoskeleton, named SEU-DER, was presented. The SEU-DER can assist the paralyzed individuals retaining preserved bilateral upper extremity function to stand up with two crutches and regain the ability of walking with an independent, functional, reciprocating gait. Based on the design principle of high-efficiency, accessibility, comfort, high safety, and the discipline of human factors engineering, we presented an original design including mechanical structure, and control and electronics system. Finally, preliminary walking assistance experiments were performed with a healthy subject to validate the feasibility and effectiveness of the SEU-DER. The experimental results prove the feasibility, reliability and assisting effectiveness of SEU-DER.