The water quality and the social economic data from 1960 to 2008 were collected, correlation analysis were used to study the relationship between the population, GDP and the TN, TP, CODMn. The results shows that there is close positive correlation between the socio-economic development factors and the Dianchi Lake's water quality, the rapid population growth and economic development is one of major reasons which cause the Dianchi Lake pollution. Caohai part was placed more severe pressure by socio-economic development than Waihai part, and the extent of eutrophication of Caohai part seems to be increasing. But on account of the Dianchi Lake's comprehensive pollution prevention and treatment, Dianchi lake's water quality has been less impacted by socio-economic development and the trend of pollution in Waiha has been basically curbed since the "The 10th Five-Year Plan of Dianchi Lake basin pollution prevention and treatment"  started in 2000.