This thesis makes an analysis of the force the hobbing bears during the boring of the shield machine and it is found out that the main reason for eccentric wear is that the resistance torque is more than the driving torque, leading to the failure of hobbing rotation. The resistance torque mainly consists of resistance moments of cutter container, earth cabin and resistance moment caused by cutter head starting. And therefore, the way to reduce eccentric wear is to decrease the resistance torque of the hobbing.