Abstract: To better analyze and evaluate the performance of the cutterhead scouring flow field for an ultra-large-diameter slurry shield, computational fluid dynamics (CFD) techniques were utilized to develop an engineeringscale simulation model of the flow field ahead of the cutterhead. The effects of nozzle inlet velocity, slurry chamber pressure, and cutterhead rotation speed on flow field distribution, effective scouring area, excavation face support force, and cutterhead torque were systematically investigated. The results indicate that the overall flow field of the cutterhead is shaped by the interaction between scouring jets and cutterhead rotation. Without scouring jets, low flow velocity in the central region increases the risk of muck accumulation and shield clogging. Within the overall flow field, the low-velocity jet was significantly influenced by the rotating flow field, leading to the formation of vortices in the central region. Higher nozzle inlet velocity expands the effective scouring area but have minimal impact on the excavation face support force and cutterhead torque. Increased slurry chamber pressure linearly enhances hydrostatic pressure and the excavation face support force, while cutterhead torque, the distributions of velocity and static pressure remain largely unchanged. Additionally, higher cutterhead rotation speed increases the effective scouring area, shifting the scouring mechanism from being predominantly controlled by the scouring jets to being increasingly influenced by the rotating flow field. To minimize interference from the rotating flow field, it is recommended to maintain the nozzle inlet velocity at no less than 4 m/s, which corresponds to a cutterhead scouring flow rate of 733 m³/h. These findings provide valuable insights for optimizing scouring system design to improve shield tunnelling efficiency.