Abstract: Consolidated cohesive soil is a kind of cohesive soil that has been deposited for a long time and formed clay minerals through physical and chemical reactions. Its starting characteristics are significantly different from those of the new silted cohesive soil, and the riverbed scouring situation is also more complicated. Taking the section of Shaoxing Urban Rail Transit Line 2 underneath the Cao ’e River Tunnel Project as an example, the method of combining flume test with river model test is adopted. The incipient velocity and sediment transport rate of undisturbed soil and model sand are measured by flume test, so as to select model sand and determine the scale of erosion and deposition time. On this basis, the river model test is used to study the riverbed erosion situation. The similarity of water flow structure and cross-section terrain erosion and deposition are verified by the measured flood and topographic data, which means that the method can accurately reflect the flow and sendiment movement phenomenon of natural river channel and the method of combining flume test with river model test can be used to predict the maximum scour depth of consolidated cohesive soil riverbed. Using this method, the maximum scour depth of the engineering river section under the action of extreme floods with a return period of one hundred years and three hundred years is studied. The results show that the upstream of the tunnel line is affected by the bend and the downstream is constrained by the left bank beach, and their scouring depth is large, while the scouring amplitude at the tunnel line is relatively small, with the maximum scouring depths of 5.5 m and 7.7 m under the action of extreme floods of once-in-a-hundred years and once-in-three-hundred-years, respectively. This method can provide reference for the design of tunnel and pipeline buried depth in consolidated cohesive soil riverbed.