Abstract: The top-level governance of mega water infrastructure projects has a profound impact on the successful implementation and efficient operation of the projects. In the process of modernizing the top-level governance of mega water conservancy infrastructure projects, accurately understanding and evaluating the effectiveness of the top-level governance of projects is a fundamental issue. Combining literature research and qualitative meta-analysis methods, we define and analyze the connotation and structure of top-level governance effectiveness of mega water conservancy infrastructure projects, and then develop and test the scale. The results show that the top-level governance effectiveness of mega water conservancy infrastructure projects is a multidimensional concept, including three dimensions of decision-making effectiveness, regulatory effectiveness and coordination effectiveness, and the scale consists of three factors and 16 items with good reliability and validity. The findings of the study help to enrich and improve the theoretical system of governance of mega water conservancy infrastructure projects, provide a scientific basis for formulating targeted strategies and improving governance effectiveness, and are of positive significance in promoting the practice of management of mega water conservancy infrastructure projects.