Abstract：Detection of contacts between 3D blocks is a key problem in 3D DDA(discontinuous deformation analysis)and DEM (discrete element method) analysis. In this paper，the limitations of the approaches commonly used to detect 3D block contacts are discussed. A new approach called penetration edges method is put forward for the detection of contacts in 3D blocks system，and the contacts between two 3D blocks are classified into seven types. The principle of this new approach is robust and can overcome the limitations of the commonly used methods. This new method can greatly reduce the amount of calculation and is easy to be coded for analysis.
