Augmented reality is the technique of transferring synthetic sensory information into a user's perception of a real environment. One of the most important tasks for every augmented reality application is to correctly merge the virtual scene and real scene into an organic whole. The implementation is heavily depended on the cooperation between augmented reality hardware and software technology. The application of affine transformation in augmented reality is investigated on the basis of analysis of traditional virtual－real registration technology based on position tracking and camera calibration. A new method for getting the relative depth of each rendered point is also put forward.