Abstract: Under the influence of global climate change and human activities, attributing river runoff changes is practically significant for the rational use and distribution of water resources. In this study, we selected the upstream areas of Yajiang Hydrological Station in the Yalong River Basin as the research area. The linear regression, Mann-Kendall test and cumulative anomaly method were used to analyze the characteristics of hydrological and climatic elements in the study area from 1961 to 2015. Based on the coupled water-energy balance principle of Budyko hypothesis, we estimated the elastic coefficient of the runoff variation corresponding to each influencing factor using the elastic coefficient method, and conducted the attribution analysis on the runoff variation. The results show that in the past 55 years, the annual runoff depth of the study area in general increased at 0.496 mm/a, and a significant change from low to high occurred in 1999. The changes of annual precipitation and potential evapotranspiration show an increasing trend at 0.994 mm/a and a decreasing trend at -0.246 mm/a, respectively. The elastic coefficients of precipitation, potential evapotranspiration and underlying surface are 1.40, -0.40 and -0.83, respectively, indicating that the annual runoff was most sensitive to the change of precipitation, followed by the change of the underlying surface; the sensitivity to the change of potential evapotranspiration was the lowest. The sensitivity of annual runoff to climate change was slightly enhanced, while its sensitivity to the change of underlying surface was gradually weakened. Climate change was the dominant factor contributing to the increase of annual runoff, and its contribution is 60.66%, in which the contribution of precipitation is 59.21%, the contribution of potential evapotranspiration is 1.45%, and the contribution of underlying surface changes is 39.34%. NDVI, which represents the underlying surface, showed a decreasing trend since 1999, and is an important reason for the increase of runoff.