Despite a rise of global concerns on climate change and adaptation in recent years, a review of articles published over the past two decades shows that research on port climate adaptation is still in its infancy (Panahi et al., 2020). Seaports play a pivotal role in the global supply chain and transportation networks and profoundly influence the regional economy and are highly exposed to marine natural disasters and climate change threats. The adaptation strategy is regarded as a practical approach to reducing vulnerabilities of the seaport to climate change. A significant research community covering various subjects on the study of port climate adaptation is emerging and forming (Panahi et al., 2020). However, the existing scholarships on port climate adaptation remain to focus on developed countries' ports and lack of diversification background. There is still a limited contribution of researchers from developing countries in port climate research. The growing leadership role of Chinese ports in global transportation and supply chain network makes researchers need to pay more attention to adaptation's status quo. In the complex context of port reform and development, in what way and to what extent do the institutions and stakeholders in the decision-making environment to China's port system affect the process of establishing and implementing adaptation mechanisms in ports, requires further research. This literature is partly formed by the work of Panahi et al. (2020). It explores the roles of and interaction between institutions and stakeholders in climate change adaptation of the Chinese port system, based on the decision-making theory. This paper undertakes an in-depth case study on Ningbo-Zhoushan port, one of China's most representative regional ports. We identify that the inadequate supply of institutions and the absence and misbehaviors of main port stakeholders cause institutional imperfection of port adaptation system to varying degrees. This paper is one of the first attempts to fill the gap in research on climate change and adaptation in Chinese ports. In addition, by bringing together concepts from social science fields into interdisciplinary research, we further prove and develop decision-making theory through case studies within the Chinese social and institutional system framework.