The commercialization of controlled nuclear fusion is gathering pace worldwide. Most nuclear fusion projects adopting the magnetic confinement fusion technology have benefited greatly from the design and engineering experience of the ITER project. The Tokamak assembly contract in the ITER project is a target price contract, dividing the project into multiple construction work packages (CWPs) that are released progressively as the project advances, and agreeing the target price for each CWP with a cap on the final payment. It is a stark contrast to the contract used in China's fission nuclear plant installation projects, which typically rely on lump sum or comprehensive unit price contracts and adhere to the traditional cost management approach known as the waterfall method. A meticulous plan is developed for these projects at the early stage, and each department responsible for a control account is held to strictly follow the planned costs, all in the pursuit of meeting the project's financial goals. Given the significant differences in contract types, this study will explore the applicability of the waterfall method to the nuclear fusion installation projects based on target price contracts with CWPs released progressively and advocates for a more flexible and adaptable Scrum agile cost management method, which prioritizes rapid response and iterative development. This Scrum method not only harnesses the strengths of the waterfall method but also considers the unique aspects of nuclear fusion projects, such as increasingly defined scopes and schedules as the project moves forward, which can significantly enhance the cost management of the Tokamak assembly project. By implementing the Scrum method in the Feeder CWPs of the Tokamak assembly project, the Cost Performance Index (CPI) of them has seen a remarkable improvement.