Abstract: Under China's strategy of fostering modern metropolitan regions, the boundary area between Shanghai, Jiangsu, Zhejiang, and Anhui has expanded rapidly through the influence of core cities. Cross-jurisdictional new towns have become emerging growth nodes for advancing regional integration. As the growth model changes, however, mismatches between spatial development and available resources have generated a hollowing-out dilemma. This paper reviews the theoretical and practical evolution of metropolitan cross-jurisdictional new towns, identifies their development paths and types, and constructs a population-space imbalance index to assess hollowing out in the study area. Three manifestations are found: housing vacancy, delayed construction, and inefficient or idle industrial space. Their causes include excessive land supply and developer land banking, multidirectional population return and aging, and internal and external constraints on industrial development. The paper proposes responses centered on multilevel governance, innovation in the use of the existing housing stock, and deeper industrial cooperation.