Researches into ancient lakes help using water resources effectively. Taiyuan, which lies in the middle of Shanxi province, had been a vast expanse of water in the pre pleistocene epoch. In the early stage of history, the water began to flow southward, and a remaining lake Zhao Yu Qi was formed in the north of Jiexiu, the west of Pingyao, Qixian and Taigu, and the east of Wenshui and Fenyang. In the pre Qin days, the lake was among the ten largest lakes in the country. Afterwards, Lake Zhao Yu Qi experienced two severe shrinkages; one happened during Han Dynasty; another happened from Tang Dynasty to Song Dynasty. Since Yuan Dynasty, the lake gradually came to be a pond and reed marshes. According to remote sensing satellite photos and images, it is found that there are three integrate spots in closed structure that are different in size. They are proved to be the changing ranges in three periods respectively. Furthermore, the stratigraphic lithology and on the spot investigatings also confirm what the historical records and remote sensing technology have shown. At the end of the paper the reasons why the Lake Zhao Yu Qi was silted up are given.