In this paper, a three degrees-of-freedom (DOFs) Supernumerary Robotic Limb (SRL) with simple structure and easy wearable character is designed. Firstly, modified DenavitHartenberg model of three-DOFs SRL is constructed. And then forward and inverse solutions of its kinematics model are obtained, and the results of kinematics model are verified. In addition, Monte Carlo method is used for solving the issue of SRL workspace, and a simulated SRL is modeled in Recurdyn simulation platform according to the actual parameters. By planning a path for the SRL, the position of the end effector and the torque of each joint can be obtained.