Consecutive rainstorm events are a main flash-flood-producing phenomenon on a basin scale, and an extreme consecutive rainstorm is more likely to cause catastrophic floods in the Huaihe River Basin. We constructed a SWAT model for the upper and middle basin of the Huaihe River and the drove model using the RegCM3 outputs under SRES A2 Greenhouse Gas Emission Scenarios, during the period from January 1,2071 to December 31,2100,to investigate the extreme streamflow response to the climate change during the flood seasons. First,we analyzed the relationship between the maximum 313 day precipitation amount and the maximum 313 day mean streamflow and determined the maximum 9 day precipitation amount as an indicator of the extreme consecutive rainstorm and the maximum 9-day mean streamflow as an indicator of the extreme streamflow in the flood season. Second,we constructed a SWAT model for the upper and middle basin of the Huaihe River to simulate the maximum 9-day mean streamflow in the flood season. Thirdly, we drove the model using the RegCM3 outputs and simulated the maximum 9-day mean streamflow during the period from January 1,2071 to December 31, 2100, under SRES A2 Greenhouse Gas Emission Scenarios and the period from January 1,1961 to December 31,1990 (reference period) respectively. Finally, we compared the results of the maximum 9-day mean streamflow in the flood season under two climate scenarios,and investigated the response of the extreme flow to climate change from the perspective of the probability characteristics. The SWAT model constructed for the upper and middle basin of the Huaihe River simulated monthly streamflow accurately based on the observational data during the period from 1958 to 2009. Simultaneously, the simulation results also reproduced the prominent characteristics of the maximum 9-day mean streamflow in the flood season. The results indicated that, under SRES A2 Scenarios, during the period from January 1,2071 to December 31, 2100: (1) RegCM3 predicted that annual mean temperature will rise, annual precipitation amount will increase, and the spatial contrast of precipitation will increase in the upper and middle basin of the Huaihe River. However, the annual precipitation amount decreased in the middle basin of the Yinghe River and showed a warming and drying trend. Simultaneously, extreme consecutive precipitation in the flood season increased, especially in the southern basin of the lower reaches. (2) The extreme streamflow in the flood season increased more remarkably, and the maximum 9-day mean streamflow in the flood season increased more than 20% on average in five hydrological gauges. ( 3 ) The probability distribution of extreme streamflow was more concentrated and the frequency of the extreme streamflow was much higher,with much higher flood risk in the middle and lower basin. (4) The probability of extreme streamflow in the lower basin responded more sensitively to the extreme streamflow changes, which means flood risks increase owing to climate change. These conclusions have practical significance for flood risk management and control in the Huaihe River Basin under the climate change scenario.