Abstract:Based on the monthly runoff data of Nuxia hydrological station in the Yarlung Zangbo River Basin from 1961 to 2015, the heuristic segmentation method was used to identify the year of abrupt runoff, and Mann-Kendall nonparametric test was used to analyze the long-term variation trend of runoff, and the concentration degree and concentration period were used to study the inner-annual changing patterns of runoff. The results indicated that: (1) The annual runoff showed a significant decrease trend first with the decreasing rate of 2.715 mm/year before 1992, and then an increase trend after 1992. (2) The runoff in the humid season accounted for 71.6%±4.4% of the annual runoff, which dominated the runoff dynamic change of the Yarlung Zangbo River Basin. After the turning point, the increasing of runoff in the dry season was another important reason for the increasing trend of annual runoff. (3) The annual runoff distribution in the Yarlung Zangbo River Basin presented a "smoothing phenomenon", that was, the occurrence time of the maximum runoff was delayed and the annual distribution was more uniform, which might be attributed to the restoration and improvement of vegetation coverage in the region. The results obtained in this study could lay a good foundation for further identifying the role of climate change and underlying surface in runoff change process, and provide practical suggestions and guidance for the sustainable development of regional ecological environment.