Visualizing software architecture faces the challenges of both data complexity and visual complexity. This paper presents an approach for visualizing software architecture, which reduces data complexity using the clustered graph model and navigates pictures of clustered graphs with constant visual complexity. A graph drawing algorithm is introduced to generate visualizations of clustered graphs. A semantic fisheye view of a clustered graph is proposed for conserving constant visual complexity. Animation is used to present smooth transition of visualizations. A case study is investigated to navigate the architecture of the Compiler c488.