Aimed at the control area of Xin'anjiang reservoir, the paper built the monthly hydrological model and calibrated and validated the model by using data of hydrological observation from 1979 to 2005. After that, the process of monthly inflow of the basion during the period of 2006 to 2099 under the scenarios of RCP2.6, RCP4.5 and RCP8.5 was predicted. On the basis of that, the variation trends of regional temperature, precipitation, evaporation and runoff in the scenarios of climate change were discussed, and the uncertainties of these variation were analyzed.The results indicated that the annual mean temperature and evaporation of Xin'an river basin show a rising trend during period of 2006 to 2099, and are sensitive to the change of radiation intensity with significant positive relative correlation between them.Whereas the annual mean rainfall and runoff fluctuate upward trend and their sensitivity to radiation intensity change is not as significant as the temperature. The annual runoff would possibly decrease in wet years and normal flow years,and showed the increase trend in dry years and especial dry years. Meanwhile, the monthly runoff shows upward trend in autumn and winter, and appears a falling trend in spring and summer.