Abstract: The Bosten Lake has been once one of the greatest continental fre-shwater Lakes．Since the large-scale land reclamation in Yanqi Basin，the human activities were causing the deterioration of ecclogical environment and the sali-nization of Lake water．In the Basin，the cultivated land is developed from 150,000 mu in 1949 to 1,243,000mu in 1980，and the diversion has taken a rise in qua-ntity from 3×10⁸m³ to 18×10⁹m³ ．According to the monitoring data，in 1982，the Basin drainage were 3.1×10⁸m³ ，and the salt discharge 680,000 tons，of which 490,000 t．entered the great Lake．The article based on a large number of the observed and analysed data，disserted in detail the evolutional mechanism of the Lake water，calculated the water-salt balance of the Yanqi Basin and the Bosten Lake，and put forward the suggestion of protecting the ecological environment of Bosten Lake.