The concept of Mapping Knowledge Domains and the Cite Space( an information visualization tool) have been got a lot of attention quickly since they are introduced in domestic academia,the relevant literature spring up like mushroom in a variety of domestic academic journals in Information Science,Science of Science and Management. But we find the knowledge visualization tool is " abused" and " misused" seriously by reading more than 500 papers that applied Cite Space,which shows that academic circles are lack of sufficient understanding of the methodology function of Mapping Knowledge Domains. The paper explains the methodology function of Cite Space mapping from four following aspects,1) elucidate its core function,changing the way we see the world,from the design concept,2) elaborate on its theoretical function of interpretation and foresight to knowledge domain,3) clarify the realization of the methodology function from applied process,and 4) introduce its application function from newly technology extension. We expect Cite Space could better develop the function of methodology in detecting academic frontiers,choosing research directions,managing knowledge and making S&T decision.