Abstract: The existing water-distribution models in irrigation canal system are established on the basis that the water discharge of the lower-level canals are equal and the cross sections of upper-level canals are unchanging with equal hydraulic power parameters, which limited the application of models. A new-type refined water-distribution model was developed, which took into account such factors as variations of water discharge of the lower canals and the conditions of section changes of the upper canals. By means of constructing reasonable fitness functions and through high-efficiency processing with the limited conditions, the model was solved based on free search algorithm. The application result showed that compared with the original way of water-distribution, water loss by this model reduced by 8.26%. As a result, the course of water-distribution was more regular and the regulating frequency of sluice gates was effectively reduced.