By means of two hydraulic model with scales 1 ∶35 and 1∶20,some physical parameters were measured ,such as flow pattern,pres sure distribution,ventilation rate and air entrainment concentration.A configura tion of outlet with aerator was recommended from comparison of some factors incl uding the height of drop,the gradient of open chute,the form of roof plate and t he size of ventilating holes etc.This figuration was adopted by the design.Fina lly,the scale effect of air entrainment on different size models is discussed in the paper. 