The construction of comprehensive index of drought was presented and the individual hydrology meteo rological elements ， such as rainfall， runoff and soil moisture content， were integrated as a comprehensive drought index using the Principal Component Analysis method. The relative anomaly characterization of drought indicators was employed to identify the drought process byRun theory. Run theory was applied to probabilistically describe the frequency characteristics of drought ， eventually to achieve a comprehensiveanalysis for the drought frequency. Then， the area above the Youxiqiao Hydrometry Station in Nanpanjiang upstream was selected as a pilot tocalculate the drought return period using the presented theories and methods and contrast to the return period of single drought index. The resultsshow that the constructed comprehensive drought index using the Principal Component Analysis method is reasonable and feasible.