Abstract: Heishiguan Hydrological Station is the control station of the Yiluo River entering the Yellow River. The variation trend of annual runoff and rainfall data series of Heishiguan Hydrological Station is analyzed by moving average method based on mathematical statistics. Kendall and Spearman rank correlation test are used to judge the significance of the variation of the series. The abrupt years of annual runoff series at Heishiguan Station are analyzed by sliding t test,ordered cluster analysis,double cumulative curve of rainfall runoff and variation process line of annual runoff coefficient. The results show that the runoff of the Yiluo River Basin shows a significant decreasing trend,and the years of abrupt change are 1965 and 1985. Because the precipitation series in the Yiluo River Basin has no significant downward trend,the decrease of runoff in the Yiluo River Basin is mainly affected by human activities such as the construction of water conservancy projects,the change of land type/vegetation coverage and the construction of irrigation canals.