Abstract: The layout of fishway inlets is affected by many factors.When the downstream river water level changes greatly the layout of fishway inlets is limited, and the fishway inlets can′t adapt to large water level variation, which lead to poor water flow conditions for luring fish.To this end, this paper sets a flow velocity regulating pontoon to improve the fish luring ability, and used a three-dimensional mathematical model to optimize the arrangement of the flow velocity regulating pontoon.The results showed that the pontoon size was closely related to the variation of the downstream water level.The flow velocity conditions in the inlet area can be significantly improved by arranging a pontoon of suitable height at the inlet of the fishway.The pontoon length and the length of the fishway inlet section had little effect on the flow conditions of the fishway inlet section.When the pontoon length was 2～4 times of the inlet width, and the fishway inlet section length was 5～8 times of the inlet width, the fishway inlet section can obtain well flow conditions conducive to the fish tracing.When the pontoon size was determined, the flow pattern was better when the pontoon was fixed away from fishway intlet at distance of 1.0～2.5 times of the inlet width.