Given the increasing number of cases where shield machines directly cut through reinforced concrete internal walls during urban tunnel construction, in-depth research on the failure mode of the internal wall during the cutting process and the load variation pattern of the cutter head is crucial for optimizing the tool configuration and improving construction efficiency. Based on the indoor test of roller cutting through reinforced concrete internal walls, a three-dimensional dynamic numerical model of the shield cutter head cutting through the reinforced concrete internal wall was established using ABAQUS. The simulation results show that the concrete mainly exhibits brittle failure, and the failure mode of the steel bars is greatly influenced by the surrounding concrete constraints. By establishing a quantitative criterion for fracture stress ratio, statistical analysis reveals that the steel bars are partial cut-off, and the proportion of complete breakage decreases with the increase in diameter. The simulation data can basically reflect the average trend of the cutter head load change in the test, with the relative errors of thrust and torque being 7.36% and 9.21% respectively. High penetration depth will cause significant load oscillation, while low penetration depth can better exert the grinding effect of the roller.