Climate change and human activities are two main factors influencing the runoff change. To some extent, climate change can lead to the spatial-temporal redistribution of water resources. The effect of climate change on river runoff yield is mainly reflected in the change of precipitation and temperature. With the increase of population, rapid development of economy and society, and the accelerated process of urbanization, a serious contradiction arise between supply and demand of water resources, and the question of water resource shortage is increasingly concerned. A prevailing thought is that research on river runoff changes should take into account the combination of climate change and human activities. In this study, Xilin River, a typical inland river basin in arid and semi-arid region of Inner Mongolia, was selected as our research object. Based on the observed data of Xilinhot Hydrological Station during 1963-2011, we used the method of cumulative anomaly (CA) to analyze the runoff sequence interannual trend of Xilin River over nearly 50 years, in order to determine the years of inflection point, i.e., 1985 and 1999. Using the revised slope change ratio of cumulative quantity (SCRCQ), we calculated quantitatively the contribution rate of the precipitation, potential evapotranspiration and human activities on runoff. With years of inflection point as a boundary, change process of cumulants of the variables was divided into three periods, 1963-1985 (T_1), 1986-1999 (T_2) and 2000-2011 (T_3). The linear regression equation was adopted to analyze the relationship between accumulated runoff and time. The slope of the linear regression equation was obtained, and then the rate of change was calculated. Compared with the benchmark stage T_1, runoff during the T_2 period decreased by 31.65%, and that during T_3 period increased by 35.75%. If not considering the effect of evapotranspiration in the area, the reduced precipitation contributed to the runoff reduction by respectively 26.30% and 57.36% respectively during the period of T_2 and T_3, and the contribution rate of human activity to the runoff reduction was 73.70% and 42.64% respectively, with the initial research phase T_1 (1963-1985) as a benchmark. On the contrary, regarding to the influence of potential evapotranspiration, the contributions of reduced potential evapotranspiration to the runoff yield change were -23.47% and -52.25% during the period of T_2 and T_3 respectively, and the contributions of human activities to the runoff yield change were increased to 97.17% and 94.89% respectively. Obviously, human activities were the dominant factor influencing the runoff yield changes of the Xilin River Basin. The human activities include population explosion, livestock grazing, industrial development, agricultural irrigation and water conservancy projects, and the influence of human activities on runoff is mitigated because of soil and water conservation projects. Since the interaction between various factors is very complex, how to further quantitatively measure influence of each factor on runoff changes need intensive study.