The impacts of human activity on Erhai Lake and their countermeasures were analysised from 1996 to 1997 in view of the deterioration of ecological environment. First, the limitation of lake resources and fragility of ecological environment wee noted after studying the background of geology and geomorphology as well as the conditions of hydrology and meteorology in the lake basin area. The major human impacts in the historical preiod involeved in the enhanced deposition, lake shrinkage and water level decline which were caused by lumbering, expansive utilization of land. Human activities in the past 50 years have damaged the lake environment seriously with the development of civilization. The successive low water level from 1980 to 1986 has lead to a disastrous consequences on Lake Ahoy. In recent years, over-exploitation of resources, industrial pollution, wide use of chemical fertilizer and discharge of domestic wastewater etc., have accelerated eu-trophication in the lake. Obviously, the intensity of human activity has surpassed the capacity of re-adjustment of the lake ecosystem. Hence, it is necessary to determine main functions of the lake in consideration of present conditions. In this paper, we suggest that tourism and supply of water be the main functions. Then, such measures as control of water volume balance, of nonpoint pollution, recovery of vegetation in the lake basin area and development of ecological agriculture should be adopted to protect the lake environment. Furthermore, human actively must he regulated in harmony with development of social economy and ecological environment through scientific administration.