The runoff observation data of major watersheds has only 50 years in China, which limits the analysis of runoff evolution characteristics. This article analyzed the runoff variation of annual and seasonal,its tendency, persistence, mutation point and period by use of runoff observation data for more then 100 years from 1909 to 2012 at Monticello hydrological station in the upperstream of Sangamon River in USA. The results showed that the annual change of runoff is greater,the seasonal distribution is uneven; the annual runoff has an significant ascent trend and a positive persistence; the mutation of annual runoff took place in 1922, 1931, 1942, 1952 and 1967; the cycles of annual runoff are 10, 23 and 56 years.The cycle of 56 years is the most outstanding and has exceeded the length of major hydrological observation data in China.