Abstract: Based on the highest water level, input water, output water and rainfall at Baiyangdian Lake in recent 50 years, the characteristics of water level changing and the corresponding reason are analyzed. Furthermore, combined with the upgrowth of Locusta Migratoria Manilensis Meyen, the effects of the water level changes on outbreak of Locusta Migratoria Manilensis Meyen were studied on the aspect of yearly and monthly changes of water level. The result shows that the water level of Baiyangdian Lake fluctuantly decreased in recent 50 years; the monthly difference of water level in a year became smaller; the reason was the decrease of input water from upriver. There exist more possibilities for Locusta Migratoria Manilensis Meyen to outbreak immediately after going back from the peak value and trough of water level. Moreover, the comparatively low water level between May and October may accelerate the outbreak of Locusta Migratoria Manilensis Meyen. The conclusions are useful for controlling storage of water at Baiyangdian Lake, predicting and preventing the outbreak of Locusta Migratoria Manilensis Meyen.