Based on model test results and weir flow calculation results, the backwater characteristics of tail bucket of ski-jump plunge pool (stilling basin) in submerged and non-submerged state are studied. It’s found that the tail bucket height should be increased on the basis of weir flow calculation because it is smaller in actual projects influenced by flow turbulence in the plunge pool. The tail bucket height can be determined by backwater curve when the flood discharge is relatively small in non-submerged state. With the increase of flood discharge, the backwater height is increasingly subject to the influence of flow turbulence, giving rise to a greater difference between the actual backwater height and the weir flow calculation result, which could reach 16.64% at the maximum. In submerged state, the backwater height is less influenced by flow turbulence, so that the difference between the actual backwater height and the weir flow calculation becomes smaller, with 7.43% at the minimum.