Wire-driven flexible robots are efficient devices for minimally invasive surgery, since they can work well in complex and confined environments. However, the real-time position and shape information of the robot cannot be well estimated, especially when there is a payload on the end effector. In this paper, a novel tracking and shape reconstruction method for a wire-driven flexible robot is proposed. The proposed method utilizes the length of the robot as well as the positional and directional information measured by an electromagnetic sensor mounted at the distal end of the robot. A reconstruction algorithm, which is based on a three order Bézier curve, is then carried out utilizing the positional and directional information along with the length information of the robot. This method can provide good tracking results and high shape reconstruction accuracy with limited modification of the robot. Compared with other reconstruction methods, the proposed method does not rely on any mechanical model of the robot. Therefore, the method works well with an unknown payload. The feasibility of the proposed method is verified by both simulation and experimental results.