With the increasing main span of the bridges across the Yangtze River, the scale of the main tower foundation and the construction cofferdam increases accordingly. Large construction cofferdams will experience different degrees of local scour during and after sinking, which will affect the construction safety of bridge pier foundations. The paper studies the local scour and protection scheme of the large construction cofferdam by the normal wide flume experiment. The local maximum scour depth and the local scour pit shape of the construction cofferdam are analyzed during and after cofferdam sinking under different hydrological conditions, and the relevant protection schemes are also proposed in the paper. Research results show that, in the process of cofferdam sinking, with the increasing of the sinking height, the local maximum scour depth increases continuously. After the cofferdam sinks into place, the local scour pits are mainly clustered around both sides of the cofferdam facing the water, and the deepest position of local scour appears at the corner of the cofferdam facing the water. The depth and range of the local scour increase with the increase of the current velocity, but the local scour pit shapes do not change obviously. In order to ensure the stability and safety of the cofferdam during construction period, it is suggested that the riverbed around the cofferdam should be protected by riprap in time after the cofferdam sinks into place.