One of the key requirements for an augmented reality system is a tracking system that determines the user?s viewpoint accurately. Many vision-based tracking systems exhibit limited tracking range due to their dependence on pre-calibrated features. Previous extendible-tracking systems only make use of point features. This paper describes an extendible tracking method that integrates pre-calibrated landmarks and natural line features for camera tracking. Extendible and robust tracking is achieved by dynamically calibrating prior uncalibrated 3D structure of line features. The experimental results indicate the effectiveness of this approach for extending the tracking range and reducing dependence on the prepared environment.