The work aims to design an express package palletizing robot for the purpose of better finishing the sorting and palletizing of express package. The complete machine three-dimensional model was established by Inventor software. The left front leg kinematic equation was established with D-H homogeneous coordinate transformation matrix. The structural optimization of the leg structure of the express package palletizing robot based on ADAMS virtual prototyping technology was carried out. The functional characteristics of rolling-type horizontal walking and adsorption-type wall climbing of the robot were respectively implemented for in-depth analysis. The sensitivity of leg optimal design variable to the angle of rotation was acquired to finally obtain the optimal leg structure. The range of motion of thigh joint angle could reach 27.34°, the height of gravity center was stable at about 340 mm, and the center of gravity was stable. The simulation results show that, the express package palletizing robot is characterized by reasonable mechanism design, stable and reliable movement, sensitive action and so on. It can be a tool that is applied in the current express industry and saves manpower and time.