Based on the nonparametric Mann-Kendall test method,the long-term changing trends and the change-points of the precipitation,the mean temperature and the amount of runoff of Huangfuchuan Watershed of the Mid-Yellow River are tested,and then the causation of the sharp decrease of the runoff within the watershed is explored with both the methods of hydrological sensitivity analysis and precipitation-runoff correlative relation.From 1985 to 2006,the climate warming and drying trend is significant therein;in which the annual precipitation exhibits a decreasing trend,but it is not so significant,while the mean annual temperature presents a rising trend,which is far over the significance level of alpha = 0.05.Meanwhile,the amount of the annual runoff also shows a significant decreasing trend with the significance level of alpha = 0.1.The testing result of the runoff change-points shows that significant changes of the runoffs of Huangfuchuan Watershed has occurred before and after 1998,i.e.,compared the natural period(19851998) with the period of the runoff variation(19992006),the amount of the mean annual runoff has decreased by 60%.It is indicated through the relevant attribution analysis that the rate of the contribution from the factor of climate change to the mean annual runoff variation is 46%,which demonstrates that the climate change is an important factor for the decrease of the runoff.