In the post-ECFA era, the marine affairs are important projects that Taiwan and Mainland China can expand and deepen the field of economic cooperation. But the marine affairs are tedious, where should both sides to start with? This article argues that both sides are most likely to expand their cooperation in the management of marine natural resources primarily, peaceful uses of international watercourses secondly, fair division of maritime jurisdiction and boundaries thirdly, and peaceful settlement of marine dispute lastly.