Large dish solar concentrator is consist of many small parabolic mirrors. In the processing and installation, small mirror will deviate from the ideal state, meanwhile some errors including non-parallelism of solar rays, tracking error etc will affect the performance of the concentrator. Based on the rotation parabolic's condenser characteristics and some previous literature's ideas. we take one part of the large dish to analysis the size of focal spot which is affected by non-parallelism of solar rays, ray tracing error, and the shift of the receiving surface position these three factors. Then, through a series of numerical simulations, we can get the analysis results which present a reference for the dish solar concentrator design and installation.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.