Abstract: A key issue in effective fish pass facility is to set up inlet for fish gathering and attraction．The main difficulty is locating migratory routes and schooling area．A flow pattern could guide fish to find the inlet．Hydraulics is combined with field investigation, in situ experiments and numerical modeling．A quantitative description is expected to build response mechanism between hydraulics and biological behavior．Habitat hydraulics (depth, velocity and turbulence) is analyzed for typical conditions from March to June, to assess fish pass facility effect and predict fish schooling．