Objective To design mechanical structure of exoskeleton which simulates physiological structure and kinematic characteristics of lower limbs according to kinematics analysis of human body, and investigate biomechanical properties of exoskeleton under two different phases of human gait period, so as to provide references for such exoskeleton design and optimization. Methods Based on clinical gait analysis of lower limbs, the mechanical structure of exoskeleton was first established by using 3D modeling software. Then the physical model was assembled, meshed and materialized by 3D modeling software, and surface to surface contact relationship between each component was also constructed to simulate and analyze the stress distributions of exoskeleton. Results Under the load of 1 kN, the maximum stress of double stance (calculating condition I) was 91.45 MPa and the maximum stress of vertical tibia (calculating condition II) was 154.55 MPa, occurring at the back support and hip, respectively, and such results were in accordance with the analysis results of force transmission mechanism got before design. Conclusions The stress distributions of exoskeleton under different calculating conditions were obviously different. Some uncertain factors such as some shock caused during the walking period, which have not been taken into account in the calculation, should be considered for the design and optimization of exoskeleton and multiplied by a certain safety coefficient.