Abstract: Augmented Reality systems often require the tracking of a user's pose in a large area to implement the registration between virtual object and the real world. To solve such a problem, this paper proposes a novel tracking system based on invisible projected markers which are created with an infrared projector. To enlarge the tracking area using only a limited number of markers, the system adopts a primary-secondary marker deployment solution, in which the primary marker uses an improved two-dimensional barcode and can be identified uniquely. The secondary marker is a simple light-spot, whose code is identified through the location relationship with the nearby primary markers and is used for the pose calculation. The system tracks the invisible markers using an IR (Infrared) camera, which means that it works in a way similar to a robust marker-less tracking system. A prototype is built to demonstrate the feasibility of the proposed tracking system, experimental result shows that the proposed system meets the requirements of accuracy for large-area tracking