Abstract: On the basis of basic theory of directional drilling and MWD technical characteristic in underground coal mine, design content, computational method and design process of directional borehole trajectory in underground coal mine were studied. By defining the basic parameters of borehole trajectory, building the coordinate system of borehole trajectory design, stipulating representing method of borehole trajectory graph, a method of directional borehole trajectory design and calculation, including plane design, section design and check was provided. Practical application proved that the method met the accuracy demands of the directional borehole design and guided drilling.