The determining of river’s headstream has always been controversial. According to the findings of several important recent scientific investigations, we analyse the causes of controversy in determining the river sources of Yangtze River, Yellow River and Lantsang River. Moreover in line with the methods of determining the river sources of international famous rivers, we explore the principles and methods of determining river source. We conclude that river length, direction, flow, watershed area and river regime are natural factors to determine the river source. At present the focus of controversy lies in the main factor. We suggest river length and direction as the main factors, flow and river regime as secondary factors, and conventional custom and cultural factors also have important influence on the determination.