Through establishing SWAT distributed hydrological model of Beijiang River Basin and taking monthly precipitation of 10 years from 13 precipitation stations within the river basin as well as the synchronized monthly flowrate data from Shijiao Hydrological Station on the main stream of Beijiang River Basin as the inputs of the hydrological model for rating of the parameters for the hydrological model, the changing law of the runoff under various climate conditions of precipitation and temperature in Beijiang River Basin is studied with the method for setting the climate scenarios. The study shows that under the impact from the temperature change of 1 % , the changes of both the annual runoff and its distribution within a year are 1 %. The impact from the change of precipitation on the annual runoff is quite significant ; i. e. under the impact from the precipitation change of 10% , the change of the annual runoff can reach to 15%,and nevertheless, the change of the annual distribution of precipitation is within 1 % with less impact. Following with decrease of temperature and increase of precipitation,the proportion of the runoff in dry season within the annual distribution of runoff is increased to a certain extent along with the increase of the inflow,which is favorable for both the safety of urban and rural water supply and the safety of ecological water demand within the basin.