Although understanding the traceability among software artifacts is well recognized as significant to multiple software engineering activities, the software traceability problem remains intractable since software engineers are very prone to get lost in the huge amounts of traceability information, and are unable to distill the required information effectively and efficiently. This paper proposes a special visualization technique – ENVISION, which is intended to facilitate major software traceability understanding tasks with viewing, navigating, focusing, searching, filtering, etc. ENVISION leverages hyperbolic tree view’s strength on elegant "focus+context" display, and compensates its restriction on net-structured data by designing a transformation from net-structured data to tree-structured data and extending the original data navigation policy. Also, ENVISION provides other useful functions like dual visualization mode, historical navigation path, round trip visualization. ENVISION is implemented in Eclipse for a traceability visualizing prototype and an empirical study is conducted based on it.