Abstract: The installation of drainage relief holes is one of the important practical measures for seepage and stability control in geotechnic engineering. But due to the numerous holes, their small diameters, and the unknown location of the free surface, the correct solution and analysis of a seepage field including drainage holes intersecting the free surface have still been a complicated problem. On the basis of the previous research work,the technique of drainage substructure is introduced into the numerical procedure of nodal point virtural flow rate to solve the above mentioned problem of free surface seepage flow with an unvariant finite element mesh. Meanwhile, many typical drainage substructures are also presented instructively. Finally, two examples analysed with the technique are illustratively given.