Also known as marine land. It is the general name of the image of internal water, territorial sea and jurisdictional waters of a coastal country. The sea area under jurisdiction includes the contiguous zone, exclusive economic zone, continental shelf, historical sea area or traditional maritime boundary outside the territorial sea. Before modern history, "Kingoma Iron" was the name of a powerful empire.

After 1840, coastal countries opened up many times, and China began to pay attention to the ocean amid the noise of the dispute between "blocking defense" and "coastal defense". The concept of blue land has long been deeply rooted in people's hearts. China has a land area of 9.6 million square kilometers. People all over China should form an idea that we still have 3 million square kilometers of blue land.

Except for internal waters and territorial waters, which enjoy the same complete sovereignty as land territory, other sea areas under jurisdiction only enjoy partial sovereign rights and interests. For example, coastal States have the right to exercise sovereign rights over the continental shelf for the purpose of exploring the continental shelf and exploiting its natural resources. However, the rights of coastal States over the continental shelf do not affect the above-mentioned waters or their legal status.

China's blue territory includes all the Bohai Sea, a part of the Yellow Sea, the East China Sea and the South China Sea, the waters around Taiwan Province Island and some international seabed areas. The total area is about 3 million square kilometers, equivalent to 30% of China's land territory. Blue land appears in popular science books or literary works, and its legal status is different from that of national territory or territorial sea.