A mirror world, which is a virtual space modeling a physical space, attracts enormous interests from VR community recently. Various applications such as Second Life, Google Earth and Virtual Earth have proven their usefulness and potentialities. We introduce a novel method to build a mirror world by acquiring environment data represented as a point cloud. Since our system provides a streaming service of the mirror world while gathering the environment information simultaneously, users located in an immersive display system can navigate and interact in the mirror world reflecting the physical world of the present state. Mobile agent which is a mobile robot carrying two laser rangefinder is responsible for exploring the physical world and creating an environment model. Environment modeling involves position tracking method to merge scattered geometric data. Optimizing method is also need to reduce space complexity of environment model.