In southeast of China, conventional geological investigations are hard to carry out due to special terrain of high and steep rock slope. In view of this, we introduce 3D laser scanning technique to collect geometric parameters(occurrence, spacing and depth) of structural planes in the surface of slope. On the basis of geological data, we establish network graphs with different strikes in association with network simulation technique of structural plane. Meanwhile, we layout artificially virtual drills on the network graph to calculate rock quality of designation (RQD). Test results show that the proposed method is of strong applicability, convenience and high reliability. It doesn’t have shortages of traditional methods by drilling core, including few data and big error of RQD. Furthermore, the method can be used in high and steep slope which is difficult for geology investigation by traditional methods. Finally, revised RQD parameters of rock mass obtained by the method meet the requirement of actual projects.