Accurate assessment of the impacts of climate change and human activities on watershed runoff is conducive to better management ofwater resources. Taking the Yongding River Basin as an example， this paper analyzed the trend of evaporation， rainfall and runoff. Mann -Kendall was used to analyze the mutation year and Hurst method was applied to analyze the degree of mutation. On the basis of this， this paperanalyzed the influence of climate change and human activities on runoff by using the method of elastic coefficient， and analyzed the reason of thechange of runoff. The results indicate that the evaporation show a rising trend， while rainfall and runoff show a decreasing trend. The mutationoccurred in 1984， and mutation degree is moderate. And the main influencing factor is the impact of human activities， and its contribution rate is72%， while the contribution rate of climate change is 28%.