Using the spatial data (DEM,land use and soil darta) and Meteorological data (precipitation and temperature data) , the Soil and Water Assessment Tool (SWAT) model was applied to the Wei River Basin (WRB) . Based on the (SWAT) model, the spatiotemporal response mechanisms of runoff to climate change were assessed in the WRB. Results show that: (1) the SWAT model has suitable application in the WRB with R2 > 0. 6,Ens > 0. 5 and Re < 20%; (2) both the climate change in the 1990s and 2000s have adverse impacts on runoff,and the runoff decrement degrees are gradually weakened from the 1990s (75%) to 2000s (50%) and from upstream to downstream; (3) the annual runoff is negatively/positive correlated with the annual temperature/precipitation; no matter the annual temperature decrease or increase 0. 5℃/1℃, the runoff change percentages are less than 3%; a 5% increase or decrease of annual precipitation would lead to a 10% ~ 15% increase or decrease of runoff respectively; (4) the runoff in spring and winter are more sensitive to the decrease of temperature,while the runoff in autumn and winter are more sensitive to the increase of temperature; the seasonal precipitation has positive impact on the seasonal runoff and the impact degree in of mainstream is greater than that in the tributary.