Abstract: This paper modified calculation method of potential evapotranspiration with modeling approach and modeling method of palmer drought severity model.According to the meteorological data of Mianyang from 1954 to 2007 and the soil moisture observation data,it established palmer drought severity model of Mianyang by using international general Penman-Monteith formula.Comparing the practical drought situation with palmer drought severity index,it showed the palmer drought severity model was effective to reflect the drought.