Any rising country in modern times all around the world must give its credit to the ocean. China, as a country with extensive territory of both land and sea, relies more and more on the sea for its soci-economic development. As a distinguished geographer, Academician Wu Chuanjun has made great contribution to the development of this academic subject of geography. He is the first one who developed the insightful theory of regional system of man-land relationship. As Mr.Wu holds, and we all acknowledge, that regional system of man-land relationship is the core of the studies of geography. Mr. Wu is also a practitioner, advocate and organizer of studies on marine geography. Studies on man-land relationship owes it to Mr. Wu, who argues that geography be targeted at the sea as well, to branch out to man-sea relationship. Mr.Wu brought it up more than once that China is such an important country boasting wide range of sea territory that geographical studies should never be limited to land territory. It is suggested that a "waterborne army" be set up to study the sea. This paper tells in detail stories of Academician Wu’s hands-on practice in studies of marine geography, of his guidance and support for young generation of geographers, and of his introducing China’s geographical studies to the international community.