Variable stiffness joint driven by wires has good nonlinear stiffness variation performance to improve the safety of interaction between human and robot. To further improve the ranges of motion and stiffness performance of robots, based on permanent magnet spring, pulley block and planetary-like gear train structure, a new type of wire-driven variable stiffness robot elbow joint (VSJPPP) was proposed. The principles applied in the joint and the structure design of the prototype were expounded in detail. The stiffness model of the joint was derived by using the static relationship between the models and the Jacobian matrix, and the stiffness relationship between model and joint was simulated by Matlab under a given condition, the variation law of joint stiffness with magnetic spring stiffness and joint position is also given. Based on the dynamic model of the variable stiffness joint, the stiffness and position decoupling controller of the variable stiffness elbow joint was designed. The prototyoe was built and the Matlab/Simulink module was used to build the block diagram of the decoupling controller to test the joint motion in different conditions. Through the trajectory tracking experiments of joint, the accuracy of the decoupled controller is verified by the stiffness and position decoupling verification experiments and the influence rule of joint stiffness change on joint position control is given. In addition, the proposed wire-driving variable stiffness elbow joint has better stiffness variation performance and motion accuracy with lighter weight and structure. While the overall joint mass is 1.51kg (excluding the driving motor), the elbow joint can rotate from -80° to 80°, and the theoretical stiffness can realize 0 to infinite variation.