Considering three major ways of SARS diffusion in hospitals, families, and public communities, a conceptual and mathematic model of system dynamics for simulating mechanism of SARS spread and control is designed. A simulation software system, called STELLA, is employed to implement the model of system dynamics of SARS in Hebei province, China. The parameters of the model of system dynamics are assigned as varied values according to the real situations and the SARS related statistical data. The experiment results show there are similar characteristics of the new report SARS cases and accumulative cases per day between data produced by simulation and by individual based investigation. Sensitive analyses of onset-to-hospitalization interval and effective quarantine are carried out, and the shortening of onset-to-hospitalization interval, it proves, should be given the highest priority. In addition, the experimental results also show that the SARS situation in Hebei province is mostly affected by the import of SARS cases from near regions such as Beijing, Tianjing, Shan Xi province, and the inner Mongolia autonomous region because there is a great flow in population among the regions in 2003.