The Tropic of Cancer is an ecological line closely touching with mankind, and takes 23°26'17"N as the standard. Its passing provincial territory certainly includes the administered land, island and sea area. In view of that relative southern latitude of the provincial territory passed by the Tropic of Cancer must be smaller than 23°26'17"N, by measuring map of Fujian sea area and integrating related arguments, the sea area administered by Fujian Province is between 23°31' and 23°09'N from the north to the south. The Tropic of Cancer passes through the sea area administered by Zhao'an County and Dongshan County of Zhangzhou City, Fujian Province, which verifies that the Tropic of Cancer passes through Fujian Province. It is ocean century in the 21st century. Under the new international normal, by analysis and demonstration on the Tropic of Cancer passing through Fujian Province, it makes us concern the Tropic of Cancer in sea area besides that on the land. Only so, it could systematically and fully discuss, recognize and manage the Tropic of Cancer.