This drought model is introduced with precipitation,evaporation as input and with soil moisture deficiency Ps as output,which can express drought clearly. The model is widely used in humid, arid and semi-arid regions and has been operated in Anhui Province and is showing dry distribution and development process in area from diurnal Ps isograph. Through diurnal Ps analysis of 31 annual hydrologic data at 4 hydrologic stations, the results achieved identify finely with the history drought of Anhui Province.