The expanding adoption of the Engineering Procurement Construction (EPC) model has introduced new challenges in project investment control and contract price management, calling for a strategic transformation in the role of project supervision. Taking a sports center EPC project as an example, this study examines the dynamic complexities inherent in fixed-price contracts during execution and highlights the operational limitations faced by traditional supervision approaches. It proposes a redefined role for supervision professionals as comprehensive investment control partners throughout the project lifecycle. A new working framework centered on risk pre-control, process auditing, and value assurance is established. Furthermore, integrated improvement measures are suggested, covering capacity building of supervision teams, evolving perceptions of clients, and supportive industry policies. These recommendations aim to enhance investment efficiency in EPC projects and promote sustainable development in the supervision sector.