Abstract: In order to use the Palmer drought severity index method(PDSIM)in the real-time large scale drought survey,the Palmer modified drought index(PMDI)of daily model is developed based on the further modification of the PDSIM by Liu Wei-wei etc.(2004).After the initial parameters adjustments of 556 weather stations scat ered in China,the countrywide daily PMDI calculation system is established.The results of one yearcs operation show its validity,and it can describe in time the large scale drought situation and its evolvement.