The temporal and regional process of knowledge spillover that has a distinct geographical performance is an important process proposed by the theory of new economic growth. Based on two case studies on the keywords of sustainable development and knowledge economy, it is found that it is improper for traditional theories to estimate the spillover intensity only by knowledge gaps. Three important findings have been discovered on the basis of the case studies. Firstly, not only is knowledge spillover related to knowledge gaps, but also the regional demands determined by geographical characteristics. Secondly, similar to many economic geographical phenomena, the space of spillover intensity is exponentially decreasing. Thirdly, knowledge driven by regional demands is active rather than the ramification of trading. Finally, a new model describing the spillover intensity between regions has been proposed in this paper. Copyright Springer-Verlag 2004O31, O33,