The Dragon King is a very popular rain god in Chinese popular religion. He is derived from both the Indian Nāga and traditional Chinese dragon. The term of the Dragon King or Longwang in Chinese character emerges in China along with the Buddhism as early as the Wei and Jin dynasties. However, till the Tang Dynasty, with the sinicization of the Buddhism and the elaboration of the Taoism, the concept of the Dragon King was given more and more Chinese elements and developed into a new figure in Chinese pantheon. The Song dynasty witnessed a further development in both the aspects of anthropomorphism and secularization with the expansion of the popular religion and approval of the government, especially conferring titles by the emperor. Till the late imperial China, the Dragon King had been a god controls all kind of waters and was known by almost everyone in China. This thesis aims to examine the formation, evolution and iconography of the Dragon King comprehensively. It not only tries to figure out the connection of Chinese Dragon King and Indian Nāga, but also draws a general picture of the Dragon King in perspectives of his history, character, image and status within Chinese Buddhism and popular religion.