Abstract: According to variation laws between borehole depth and orifice feed pressure found in consequent landslide directional drilling of hard limestone in Zhangji Coal Mine, back pressure phenomenon appeared at 400 m to 500 m hole depth. Theory of the drill string elastic feeding theory was used to analyze the mechanism of back pressure effect, which explained the law found in the consequent landslide directional drilling of the hard limestone in Zhangji Coal Mine. The main effect of the generating back pressure effect was due to the influence of drilling friction. On this basis, the influencing factors of the back pressure effect were analyzed. The main influencing factors were: formation lithology, curvature and displacement, vertical depth and cuttings, hole depth, self-weight and feeding pressure. And from the perspective of reducing the influence of slide directional drilling on the hard rock layer, the optimization suggestions were given in reducing the friction of the drill string and the hole wall, developing the anti-friction and drag reduction tool, compound drilling.