One unsolved problem in the development of an effective welding training simulator is how to construct an accurate 3D welding torch model based on the moving position of this torch in the training process. This paper presents an effective approach to deal with the problem. The whole scene is constructed in the base coordinate system and the torch is modeled as a 3D object in the sub-coordinate system. The sub-coordinate system firstly overlaps the base coordinate system, and it’s continuously changing as the trainer operates the torch. A nine axis sensor is installed in the torch at a selected point, which is the origin of the sub-coordinate system. The sensor can measure the rotation posture of the torch. Another marked point that can be captured by the Binocular Vision System (BVS) is installed with an infrared emitter. The BVS can measure the coordinate values of this point in the base coordinate system. As long as the coordinate values of a certain point on the model and its rotation posture based on this point can be determined, the VR development tool, such as Unity-3d,can track the model in real-time. That is the algorithm of this system, which is verified by Pro/E, a 3D modeling software. The approach presented above is applied to a welding training simulator product, which has been put into use and proved to be effective.