A Web graph refers to the graph that is used to represent relationships between Web pages in cyberspace, where a node represents a URL and an edge indicates a link between two URLs. A Web graph is a very huge graph as growing with cyberspace. To use it for Web navigation, only a small part of the Web graph is displayed each time according to a user's navigation focus. The graph layout has always been a challenge for visualizing systems. In this paper, we present a visualization system of an online Web graph, together with the methods for clustering and filtering large graphs. In this system, a Web crawler process is used to get on-line information of the Web graph. Filtering and clustering processes reduce the graph complexities on visualization. In particular, the filtering removes those unimportant nodes while the clustering groups a set of onnected nodes and edges into an abstract node. The visualization process incorporates graph drawing algorithms, layout adjustment methods, ...