Abstract: The performance of twenty-two General Circulation Models(CCMs)in simulating precipitation and temperature are evaluated and validated in the Yangtze River basin.Simulations of these CCMs were used in the IPCC Fourth Assessment Report(AR4).The Bjerknes Center for Climate Research(BCCR)Bergen Climate Model (BCM)2.0,or BCCR_BCM2.0,and other six CCMs stand out from the twenty-two evaluated CCMs.Using an artificial neural network and climate changs projections from the selected seven CCMs under A1 B,A2 and B1 scenarios, the hydrological response to future climate changs in the Yangtze River basin is studied.The projective on the subject is presented.The result shows that there could be a decreasing trend in the mean annual streamflow in the future.At the Yichang station,a dry year condition would be likely to become more common in a warmer world.The reduction of mean annual streamflew could reach as much as 520 m³/s for dry years,while such a reduction would be 250 m³/s for a normal year at the Datong station.The decrease in available water could be a bid challenge to the practice of water allocation and management in the western and central routes of the South-to-North Diversion project.The mean monthly streamflow would be projected to be increasing during January to June,while,the opposite should be true during the second half of the year.At Yichang and Datong,the streamflow increases would be 29.6% and 13.8% during,Tanuary to,Tune and decreases could reach as much as-18.2% and-11% during the second half of the year,respectively.The variation of streamflow could he expected to be larger at Yichang than at Datong.During flooding seasons,there would be a decrease of-8.5% in Yichang streamflow,and a slight incerease for other reasons.In contrast,the Datong streamflow would have a 2.3% increase during flooding seasons,and a slight decrease in non-flooding seasons.