Abstract　 　　 

　The Large Synoptic Survey Telescope (LSST) is a 8-meter class wide-field telescope that is designed to conduct a decade-long time domain survey of the optical sky. With its 3.5 degree field of view, it will cover half of the sky every three nights.  In order to realize the scientific potential of the LSST, its optical system has to provide excellent and consistent image quality, in terms of both the image size and ellipticity. The LSST will utilize an Active Optics System (AOS) to optimize the image quality by controlling the surface figures of its three mirrors and maintaining the relative positions of its optical elements. In this talk, I will present our ongoing effort to build an integrated model of LSST, and demostrate how we use this model to test the wavefront sensing algorithm, to develop an effective AOS control strategy, and to verify the system performance against the image quality error budgets. It will also be a very useful tool for future trade studies, commissioning, and for understanding systematics in scientific analyses such as weak lensing.