Lake Yuxingze is a famous ancient lake in China because it was recorded in a Chinese classic geography book of The Tribute of Yu (Yugong) and there have been some different opinions about its location, age and forming conditions. Based on the documentary records and field investigations, we study systematically the lake-appearance stratum in the trough wash of Xingyang region, including the geological conformation, the distribution of stratum and the ancient geographical surroundings. Especially according to the data of measured ¹⁴C age, we think that this lake-appearance stratum had been made from the ancient lake described in The Tribute of Yu (Yugong) saying that the Jishui River flowed into the Yellow River but when it flooded, the name of this area was Xing, so we call this ancient lake the Lake Yuxingze. This ancient lake functioned actually as a natural flood detention area of the Yellow River then.