Abstract: RQD, as an important parameter to reflect the rock mass quality, has been applied universally and played an important role in geological engineering and geotechnical engineering. There is an apparent defect for obtaining RQD values through drills. The RQD values vary in different directions. RQD through drills whose direction is perpendicular to the ground can not represent that in the rock mass. In this paper, the three-dimensional fracture network simulation is employed to calculate RQD. Scanlines, represented by the actual drill, are set in the rock mass, and RQD in different directions can be obtained. The rock masses are different from other materials, and the RQD values are different considering different points in the study rock mass. It is not considered in the former studies. The number of the optimum scanlines is studied. The results show that when the scanlines in x, y and z directions are 25, 80 and 55, the RQD values are real and the computing time is the minimum.