Water level in Lake Qinghai, a representative inland lake in northwest China, is declining rapidly under the influence of climatic change. At the same time, the environmental problem becomes more serious. It has arrested many people's attentions. In this paper, the stream flows for period until the year of 2050 are estimated by multiply linear regression and the trends of the water level are forecasted based on an improved model of hydrologic and energy balance. The prediction indicates that the water level would keep steadily about 3192.7m before the year of 2020, and then continues to decline. It would drop to 3191.22m in 2050. Changes of the water level in Lake Qinghai would become alleviative in the next several decades of 2010-2050.