Abstract: The characteristics of fish convection field were analyzed by in-situ observation and numerical simulation. The numerical simulation model of the flow field downstream of the dam of Cuijiaying hydroproject is constructed to calculate the downstream flow field of the hydroproject under different operation conditions in the migratory season, and the distribution characteristics of water depth, velocity and other hydraulic elements are counted. Based on the observation of the downstream fish cluster distribution in the same period, the response relationship of fish cluster to the flow field is revealed through the comprehensive comparative analysis of fish cluster distribution and flow field characteristic distribution, and the response of fish cluster to the flow field is proposed. The preference curve of flow field characteristics provides support for the scientific formulation of ecological dispatching scheme of Cuijiaying hub and the construction of other similar ecological dispatching projects.