The model of mathematical relationship between water and soil pressure on shield and gradient of slope is established; the mathematical relationship between shield thrusting resistance and slope gradient is deduced; the shield thrusting resistance when boring horizontally and downhill by 6° are calculated; and the curves of relationship between shield thrusting resistance and slope gradient are described by software MATLAB, by taking shieldbored inclined shaft of Xinjie Mine in Inner Mongolia for example. The results show that: 1) Compared to boring horizontally, the total thrusting resistance of shield when boring downhill by 6° is 8% smaller. The total thrusting resistance of shield when boring downhill by 6° nearly equals to that subtracting component of gravity along axial line from total thrusting resistance of shield boring horizontally when the gradient is less than 13°. 2) The total shield thrusting resistance decreases with the gradient increase. 3) The shield will slide downhill when the gradient is larger than 50.4°； as a result, the cutters on cutterhead would be invaded into excavation face which would induce hard torque start and cutter replacement.