It is of great important significance to study the mechanism of initiation

propagation and coalescence in engineering rock mass and the subsequent sliding mechanism along the weak structural plane for revealing the law of deformation and failure of rock mass. Discontinuous deformation analysis（DDA） method owns an inherent advantage in simulating the sliding deformation of discrete block system

which is formed by the intersections of various macroscopic structural planes. But it is slightly inadequate in the simulation of the evolution process from continuum to discontinuum. DDA has strengthened its ability in the simulation of continuous characteristics of rock mass to a certain extent by introducing virtual joint technology to discretize the continuous area into sub blocks and then setting strength of virtual joint as that of the rock itself. However

this treatment only considers the bonding effect of virtual joints before reaching the tensile strength and ignores the strength of the strain softening stage in the complete stress-strain curve of rock. Therefore

the above deficiencies have been improved by inserting a so-called strain softening cohesive element between the sub blocks which can describe the strain softening stage in the stress-strain curve of rock. This further strengthens the ability of DDA in the simulation of continuous attributes of materials and also retains its inherent advantages in the simulation of discontinuous deformation. Finally

it is applied to solve several typical crack problems. The results show that the simulated fracture paths are in good accordance with the reference solutions

proving the validity and correctness of the improved DDA method.