Bakeyao Lake is located in the Horqin Sand Land, in the eastern part of Inner Mongolia. In estimating the dates of the lake sediment, the author found that the radiocarbon dates were nearly 2000 years older than thoes derived from²¹⁰Pb measurements. In order to find out the reason. the author made sonce investigations on some other carbon dating results for lake sediments in the arid and semi-arid areas of China,and found that most of them seemed to be 1000-2000 years older than expected. This makes the author conclude that the usually older dates derived from the radio carbon dating may have been induced by the “hard water” effect.Caution therefore should be paid to the carbon dating problem in the future studies in North and West China.