The invention discloses a shield tunneling machine for ultralarge U-shaped cross sections. The shield tunneling machine comprises a cutterhead device, a driving system, a shield structure, a main propelling system, screw conveyors, an equipment bridge, a backup system and a continuous belt conveyor. The cutterhead device is formed by nine spoke-type cutterheads, and driving shafts of the spoke-type cutterheads are parallel, wherein a medium-diameter spoke-type rear cutterhead is positioned at the center of a rear plane, three large-diameter spoke-type front cutterheads are positioned on two sides of the upper portion and the bottom of the middle of a front plane, three large-diameter spoke-type rear cutterheads are positioned on two sides of the upper portion and the bottom of the middle of the rear plane, and two small-diameter spoke-type rear cutterheads are symmetrically distributed at arch edge of the upper portion of the rear plane. The shield tunneling machine can be used for excavation of arched U-shaped cross sections of curved walls and is small in excavation dead zone and adaptive to geology of loess, silty clay, clay, silty sand, soft rock and the like, and the area utilization rate of tunnel cross sections is greatly increased. In addition, by the shield tunneling machine for the ultralarge U-shaped cross sections, construction cost is greatly reduced while construction efficiency is effectively improved.