The water flow conditions at Qiantang River estuary are complex, with a large range of riverbed erosion and siltation. Water flow erosion may cause erosion at the foot of the cofferdam, resulting in the collapse of the cofferdam. Using physical model experiments to study the anti erosion effects of different protection schemes is of great significance for the rational formulation of construction plans. Taking the first phase of the expansion of the western channel (north-south line) of the Hangjiahu south drainage project as an example, four physical model tests were conducted to analyze the distribution of erosion and sedimentation near the cofferdam and the maximum depth of erosion, including unprotected, stone throwing protection, reinforced gabion, and stone throwing & reinforced gabion. The results show that the horizontal anti erosion effect is related to the anti-strike effect of the surface layer and the filtration effect of the bottom layer; The reinforced gabion scheme has poor anti erosion effect, resulting in bottom layer poor filtration effect. The riprap and riprap & reinforced gabion scheme have both the ability of surface layer anti strike and bottom layer filtration, so the protective effect is better. The research results can provide reference for the formulation of protection plans during the construction period.