Heilongjiang is an international river that flows through Mongolia, China and Russia, and is located in the northeast of Asia.

Heilongjiang is divided into north and south sources, with the Ergon River as the source in the south (in China) and the Krulun River as the source in the north (in Mongolia), and finally flows into the Okhotsk Strait, and the sea mouth is in Nikolayevsk, Russia.

Heilongjiang was originally the inland river of China, and it became the border river between China and Russia after Russia forcibly dominated a large territory north of Heilongjiang and east of Wusuli River in China in the middle and late19th century. In 2004, China and the Russian Federation signed a final border agreement, with Heilongjiang as the basic border, and defined a clear boundary between the two countries.