By using meteorological data in the area of the first meander of the Yellow River and data of both annual runoff in the upper reaches and the cutoff in the lower reaches,climate changes in the meander area and their effects on annual runoff in the upper reaches and the cutoff in the lower reaches were analyzed.Results showed that in the meander area, annual precipitation tended to decrease and fluctuated in three periods of 2-4,6-7 and 10-11 years.The mean annual temperature was remarkably greater than that of other areas in China.The departure of annual temperature was low before 1983,and high after 1984.Annual runoff of the Tangnaihai fluctuated in two periods of 4-5 and 14-16 years.The waves for annual precipitation in the meander area and annual runoff of the Tangnaihai were basically agreed.The mean annual temperature was high,sometimes,whereas annual precipitation and annual runoff were low in 1990s.The fluctuated trends of annual precipitation in the meander area and the cutoff in the lower reaches were on the contrary.The climate changes in the key and sensitive area of the upper reaches of the Yellow River greatly affect the water resources of the region.