Abstract: In order to solve the issue of spatial block identification of finite structural planes under complex geometrical boundaries, the geometric modeling concept of sagittal planes is proposed and the meshing method is introduced to the block theory. Firstly, the rock mass is meshed into small independent elements. Then the structural planes are added orderly and the elements are cut after the contact judgment. Finally, the independent spatial blocks are formed when the mesh is removed and the elements are united. The cutting method of blocks with arbitrary configurations is given by planes. Based on the merger of directional edge, the merging method of the same direction and opposite surface is united aiming at block merging. The results show that it has good advantages for the dynamical appending of structural planes and the building of complex geometry model. Moreover, there is no limit to the form and number of block identification, and the programming progress is simple. The prosposed method is further illustrated with its application to tunnel engineering in Liaoning Province. All of the independent spatial blocks are identified, and then the information of the key blocks is obtained. Its effectiveness and superiority in complex block identification is demonstrated through the engineering practice. It may provide technical support for the safety production of rock mass engineering.