Abstract: The relationships between the populaton of Yangtze voles ( Microtus fortis ) and the evolvement of the Dongting Lake beaches were analyzed based on historical data,and the impacts of the Three Gorge Engineering on beach environment and water level of the lake were assessed according to the regulation scheme on downward discharge flux of the Three Gorge dam.The results indicated that the population of the voles has been increasing since 1950's,owing to the continuous enlargement of the lake beach and prolonging successional emergence of the beach.The emergence date of the beach in Autumn would be earlier,its emergence area would be going up,the population of the voles would be also expanded at the initial post construction stage,which would still increase with the continuous expansion of beach area in a middle and long period after the establishment of the dam.More voles would thus move to the farmland,and heavily harm crops.

Key words: Microtus fortis, Population, Three Gorge Engineering, Dongting Lake