By restructuring its planning system and integrating competences of land resource and water management, environmental conservation, agriculture, as well as spatial planning, under a same Ministry of Natural Resources in 2018, China ambitioned to definitively turn the page on inconsistent and sectoral planning practices. However, existing planning instruments are still linked to administrative boundaries and remain statutory and regulatory in nature, which makes them inadequate to address complex and dynamic megacity regions that span across different administrative entities. The Yangtze River Delta megacity region is the subject of an ambitious integration plan which focuses on economic coordination and urban services, however, there is still no coherent vision on its spatial development at the territorial scale. This article presents the “Jiangnan Park,” a university-led and design-driven research project focusing on the vast triangular plain between cities of Shanghai, Hangzhou, and Suzhou. Using the encompassing metaphor of regional “park” and applying the emerging method of regional design, this project combines mapping, visualization, design strategies, and workshop techniques to elaborate a development vision for this historically and ecologically sensitive area. As a pioneering case of regional design in China, this project exemplifies how the use of cross-scale and cross-sectoral collaborative methods can inform the development of integrative strategies for complex megacity regions.