During slurry shield tunneling, the mud cake phenomenon often occurs on cutterheads, which should be effectively solved while ensuring their structural strength. For example, in Yuanjiang Rivercrossing tunnel in Changde, China, a targeted design is tested on a cutterhead arm in soft soil under atmospheric pressure. First, the cutterhead structure′s effect on muck fluidity is analyzed. Then, the cutterhead structure is optimized based on a sensitivity analysis method, and finally, the optimization results are evaluated. The obtained results are as follows: (1) Considering the cutter configuration and installation layout, the cutterhead structure with five arms remarkably improves the muck fluidity at its center. Therefore, the opening size should be gradually increased from the center to the periphery. (2) From the sensitivity analysis results, the front panel of the cutterhead and the support plate of the tool changing box significantly affect the stress on the cutterhead. Hence, increasing their thickness can significantly strengthen the structure of the cutterhead. (3) The proposed optimal design method of the cutterhead can reduce its weight and enhance its mechanical properties.