The drought evaluation is taken as an important step of drought disaster monitoring and defense.How to accurately assess and predict drought conditions is the hot and difficult point of current research in study area.Based on the hydrological and meteorological data in the upstream of Luojiamiao of Zishui river basin,the paper computed the drought indexs of different time scales, and then constructed the short term/long term composited drought index by using the principal component analysis method.The result revealed that the short and long term composited drought index can best recognize the history drought of Zishui river basin.The result may provide the important reference for the construction of drought disaster monitoring and defense system in Yangtze river and other basins.