Adjacent ports played a significant role in the evolution of the port system. In our study, we selected five pairs (i.e., Dalian-Yingkou, Qingdao-Yantai, Shanghai-Ningbo, Xiamen-Quanzhou, and Shenzhen-Guangzhou) of the most important adjacent ports in China to reveal the recent trend of China unique port system development; how and why will port system development be de-concentrated; and integrate the conceptual modal into in-depth analysis. The major findings are as follows: (1) There is functional differentiation in adjacent ports. To some big ports' sustainability, they focus on foreign trade while other small ports, in order to achieve sustainable development, they focus on domestic trade; (2) First-mover advantage and dislocation competition is a mechanism of China ports functional differentiation; (3) Shanghai and Ningbo are unique in that both ports are similarly focused on foreign trade because they both have deep-water harbors, excellent geographical location, export-oriented hinterland economy, and close foreign investment relationships.