Under the impact of global warming, China Water Tower is undergoing warming and wetting dominated climate change. Affected by the influence of climate and underlying surface conditions, the water resources increased significantly in this area, and the runoff mechanism showed obvious regional differences. Based on the data of hydrometeorological elements in China Water Tower from 1956 to 2020, we analyzed the hydrological elements, the change and trend characteristics of runoff capacity, as well as the mutual influencing mechanism among them, using trend, abrupt change and anomaly analysis methods. The results show that during the study period, the air temperature and evaporation capacity have all increased, resulting in a significant increase in precipitation and runoff, which indicates that the study area has entered the wet season. At the same precipitation and runoff scale, the runoff capacity decreased in the source area of the Yellow River, but increased in that of the Yangtze River and Lancang River. The increased temperature, continuously abundant rainfall, initial rainfall increase of the basin, increased runoff in dry season and enhanced ecological water holding capacity of the underlying surface are the main reasons for the change of runoff capacity and the increase of water resources in China Water Tower area.