Maritime regional cooperation has its own unique internal mechanism, for which Marine Regionalism is the theorization and provides an analytical framework. Marine Regionalism covers two layers: the legal basis for regional cooperation in global law of the sea, and the specific cooperation regime in a particular region. There is an interaction mechanism between the two layers and the UN specialized agencies play a pivotal role: the global law promotes the establishment and development of regional cooperation regimes, and regional issues raised by or regional measures adopted by regional cooperation regimes, at the same time, may also promote the evolvement of global law. Taking the Vision for Maritime Cooperation under the Belt and Road Initiative as a clue, the paper proposes some thoughts and suggestions on maritime cooperation under the Belt and Road framework from the perspective of the development mechanism and trend of Marine Regionalism. Firstly, China may consider ratifying the 1995 Fish Stocks Agreement which provides the legal basis for regional cooperation. Secondly, China should attach importance to the pivotal role of the UN specialized agencies especially the IMO. Thirdly, China can promote regional cooperation in the South China Sea based on the Semienclosed Sea Articles. Fourthly, China may participate in the regional marine cooperation regimes along the 21st Century Maritime Silk Road in a bottom-up way.