Abstract: Metropolitan areas are pivotal in regional coordinated development within urban agglomerations, nonetheless, imbalances among them remain underexplored in academic research. In the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), the "Shenzhen-Dongguan-Huizhou" (SDH) and "Zhuhai-Zhongshan-Jiangmen" (ZZJ) metropolitan areas, initially comparable parity in geographic proximity and resource endowments during the early years of reform and opening-up, have diverged significantly, with SDH achieving substantial developmental advantages over ZZJ. In light of the interplay between top-down policy directives and local responses as the hallmarks of China's governance, by adopting the policy accumulation framework, this study investigates the roles of policy density and policy scale in shaping these disparities across four policy domains—innovation, industry, funding, and talent—between 2000 and 2022. The findings indicate these imbalances can be attributed to three key dynamics: vertical escalation of policies, horizontal disparities in policy accumulation, and uncoordinated accumulation of policy evolution. This research advances the insights of disparities among metropolitan areas in terms of policy aspects. By offering the associations and mechanisms of policy-induced imbalances, the research provides a competitive framework for urban governance and policy analysis.