In order to study the scale effect of aeration in a scaled model of flood discharge and energy dissipation, as well as to get more accurate test data, the shape of the air jet and the aeration quantity(volume fraction)in a plunge pool with hydraulic models of scale 1∶100 and 1∶50 are studied and compared. The experimental results show that the air jet diffusion in different scaled models is very different from each other, although with the similar orifice shape. The air jet scatters into the plunge pool in an arc shape for the 1∶100 model while it scatters in an ellipse shape for the 1∶50 model. Differences of the air jet patterns further lead to different air entrainment quantity in the plunge pool. The air entrainment quantity in the jet impact area for the 1∶100 model is higher than that of 1∶50 model, and the peak air entrainment quantity is about 50% for the former while it is about 40% for the latter. Comparison of the spatial distribution of the air entrainment quantity in the plunge pool shows that aeration of 1∶100 model has a relatively smaller lateral distribution and a relatively larger vertical distribution.