Since the analysis of seepage field with horizontal drain holes and the stability analysis of reservoir banks are very complicated, the application of horizontal drain holes in the engineering control of bank slope is restricted seriously. It is economical and reasonable to add horizontal drain holes to improve the slope stability, so it is of both practical and theoretical significance to research horizontal drain holes. Considering the complication of analysis, the paper introduces a complete set of methods of establishing the model of horizontal drain holes, analyzing the seepage field with horizontal drain holes and analyzing the slope stability after engineering control with horizontal drain holes only in twodimensional condition with a calculation example. The results of numerical analysis show that the slope stability can be improved by adding horizontal drain holes. and the length of the hole has obvious effects on draining compared with the aperture.