Flood classification in fact is an optimum problem for recognizing the magnitude of flood intensity. Flood classification will not only affect the real operation of reservoir, bus also influence the risk evaluation of flood disaster. For a reservoir which uses precipitation forecast to carry out floodwater utilization, flood classification plays an important role in proposing the real opera- tion rule under the condition of floodwater utilization. Therefore, flood classification is very important in theory and practice. Tak- ing representative Yichang Hydrometric Station for Three Gorges Reservoir on the Yangtze River as an example, the flood classifica- tion optimum model is supplied based on project pursuit method, and the model is solved by particle swarm optimization algorithm. The results illustrate the validity and reasonability of two combined methods applied to flood classification.