Robots capable of jumping need higher torque drive and more stable and reliable mechanical structure. We designed a medium-sized robot leg with excellent jumping ability, and adopted parallel rod structure in the mechanical structure, and established a simplified model to analyze the structure. The mathematical model is established by using the objective design method for simulation, and the optimal driving scheme is determined by the simulation results. Lightweight materials and lightweight design have been used to minimize weight. Moreover, a prototype of the parallel leg is developed, on which the loaded vertical jump experiments are achieved. The results of experiment validate the ability in loaded jumping of the robot leg, which could implement a vertical loaded jump in maximum jumping height of 82cm and achieve continuous and stable jumping.