Abstract: Based on the principle of constructing independent blocks by overlapping， the paper discusses the problem of blocks searching. And the overlapping principle and method of the surfaces with the same and opposite directions are studied. At the same time， the cutting and searching process of blocks is given， which includes the meshing of three-dimensional structural surface， the analysis of intersection about structural plane and boundary， and the searching of key blocks. Based on the principle of overlapping technology， a new searching technique is proposed for identifying the key blocks. With the searching technique introduced into the 3D digital analysis system—the three-dimensional geotechnical structural modeling and analysis system (GeoSMA-3D) developed by ourselves， the searching technique is available to identify the key blocks. Meanwhile， an engineering application is performed to validate the effectiveness of overlapping technology and the superiority of GeoSMA-3D software.

Key words: overlapping technology, block searching, GeoSMA-3D, key block, program development