Abstract: The characteristics of strain calculation in discrete media were analyzed.Based on the ‘equivalent continuum’ approach,a modification was made to the spatial triangulation method,similar to the updated Lagrangian method in continuum mechanics.A nonlinear meshfree interpolation method was suggested to calculate the strain in discrete media and a brief verification was made in two-dimensional case.It was indicate that the calculated strains were well matched to global strain and more suitable for problems involving localizations such as shear bands,compared with those obtained by spatial triangulation method.