Abstract: Using runoff data of Tangnaihai Hydrometric Station, meteorological observational data including temperature, precipitation and evaporation and climate indexes such as plateau monsoon and westerly circulation from 1961 to 2021, the characteristics of runoff in the upper reaches of the Yellow River were analyzed to uncover the climatic causes that affect the runoff change. The results show that the runoff in the upper reaches of the Yellow river had a sudden change from descending to rising around 1991, and it has increased significantly since 2001. The runoff has a significant change period of 8 years. Climate warming and wetting is the main reason of the abrupt runoff increase and the transformation of atmospheric circulation and its influence is an important reason for the significant increase of runoff in the upper reaches of the Yellow River. Runoff has increased in the upper reaches of the Yellow River since 1991 under the joint action of the weakening of dry westerly circulation and the enhancement of warm and humid plateau monsoon.