The variation of Lake water level and its environmental change are unavoidable processes under climate changes and human activities in arid regions. In this paper, the variations and driving forces of water level of the Bosten Lake, the largest inland fresh water lake in China, were studied based on the observed hydrological, metrological and social-economic data of the lake during 1958-2012, and Gray correlation analysis was employed as an effective methodology to discriminate potential contributions of natural and social-economic factors to level fluctuating of the lake. The results showed that:(1)The lake experienced three phases of water level fluctuating such as forepart falling, then rising and declining again with different driving weights over the past half a century; (2)Results of Gray correlation analyses showed that, the variation of water level of the Lake was caused mainly by the co-effects of the variations of natural factors such as flows into the lake, precipitation and temperature, and human factors such as the changes in farmland area, especially, the variations of flows into the lake was the main driving factor that effects the variation of water level. Because of Kaidu River runoff kept low flow state during 1958-1987, the water level of the lake has slowly declined, the water level of the lake decreased from 1 048.00 m in 1958 to 1 045.03 m in 1987, the average water level was about 1 047.20 m above sea level. The climate change is the most important factor to influence the declination of the lake level during this period; Kaidu River runoff kept high flow state during 1988-2002,and surface water inflow to the Bosten lake has increased. Contemporary,lake level raised significantly, the water level of the lake raised from 1 045.21 m in 1988 to 1 048.60 m in 2002, the average water level was about 1 046.80 m above sea level. The impact of human activity on the water level during this period began to increase, but the impact of natural factors is still stronger than the impact of human activities on the water level; surface water inflow into the Bosten lake decreased remarkably during 2003-2012, lake water level also showed a sharp downward trend, the water level of the lake decreased from 1 048.55 m in 2003 to 1 045.68 m in 2012. The impact of human activities on the water level during this period showed a significant increasing are trend; (3) For the encompassing period of 1958-2012 with over half a century period, the main driver factors of water level variation transformed from climate change to social-economic development related human pressure.