Abstract: Seepage flow numeration is an effective tool for simulation,dynamic analysis,effect evaluation and forecast of drainage process in rockmass.The dynamic process of the roadway drainage in the side slope is simulated by using boundary element numerical method.Resultsshow that seepage flow coefficient tensor and drainage porosity of rockmass have an obvious effect on the drainage and the dynamic process,as well as the boundary element numerical method is effective on the drainage simulation of small section in size.