Abstract: Using a simple water balance model,monthly runoffs were simulated for 21 catchments with different climatic conditions in China.The sensitivity of runoff to climate changs in these catchments was further studied for hypothetical climate changs scenarios.Results show that monthly runoffs can be well simulated by the simple water balance model,the Nash-Sutcliffe coefficient on these catchments are greater than 65% and the corresponding average relative errors are less than 1%,and there is large spatial variations in the sensitivity of runoff in response to hypothetical climate changs scenarios.It appears that runoff is most sensitive to the changs in temperature and precipitation in arid and semi-arid catchments over the north Yellow River region,the sensitivity is less significant in humid and semi-humid catchments over regions of Central and South China,while almost no sensitivity in alpine regions in West China.Thus,the climate changs adaptation in the water sector should focus on arid and semi-arid regions in China.