In order to solve the problem of the prototype observation for the complex flow field at the entrance area of downstream approach channel of navigation structures，we invent a new method to measure the flow velocity and field more precisely，and obtain the transverse velocity，longitudinal velocity and reflux velocity at the entrance area of the downstream approach channel of the ship lift under different flow conditions and reveal the characteristics of the flow field at the entrance area of the approach channel with permeable guide wall，which provides an important basis for navigation safety evaluation of ship lift and optimization of route and navigation method. Comparing the results of prototype observation and model test，we put forward some suggestions for the model test of navigable flow condition and the evaluation of ship navigation safety，which can provide reference for related research.