East Sea of China. In the Eastern Han Dynasty, Cao Cao used the word "the sea" in his poem "Looking at the Sea", describing the scene of Cao Cao climbing Jieshi Mountain to see the sea. Since then, the word "sea" has been widely used and has become a common vocabulary for the sea in Chinese. China East Sea refers to a large sea area outside the Yangtze River estuary in eastern China, which is located in the northwest of the Pacific Ocean and consists of the Yellow Sea, the Bohai Sea, the Japanese Sea, the East China Sea and the South China Sea.