The bias-corrected and spatially and temporally downscaled(BCSD)method was used to downscale 20 GCM in IPCC AR4 in an A1B scenario in the source region of the Yellow River based on the data of daily precipitation, daily temperature, maximum temperature, and minimum temperature from 16 meteorological stations during the baseline period from 1961 to 1990. The performance and the confidence of BCSD are demonstrated in brief. The downscaling results show that, in the future, in the source region of the Yellow River, the temperature will increase by 0. 032℃ per year and the precipitation will increase by 0. 50 mm per year, with fluctuations and a slightly increasing trend, in the A1B scenario. Meanwhile, the temperature and precipitation are increasing significantly in the southeastern area, indicating that the climate there is becoming warm and humid.