Abstract: Two major current issues of discrete element method(DEM)in rock and soil fields are proposed：1)mechanical relationship between discrete particles and macro model is not clear; 2)DEM requires huge computation, and it is low in efficiency. Theoretical studies and software development are carried out for the two issues. On the basis of the particle contact model of DEM,conversion formulas are introduced to build discrete element model with specified mechanical properties; a method for energy calculation of discrete element particles is also proposed. Based on these theoretical studies, a three-dimensional discrete element simulation system of rock and soil,MatDEM,has been developed from scratch. The software has good pre-processing and post-processing functions, with which result images and simulation demos can be generated automatically. Furthermore, the speed of DEM calculation is improved significantly using matrix calculation and high-performance GPU(Graphic Processing Unit) computation. MatDEM was used in the numerical simulation of hydraulic fracturing in a rock pore. Dynamic simulation of one million particles was completed in a single computer. The result indicates that micro-cracks tend to form along direction of maximum compressive stress and weak directions of anisotropic rock. Energy conversion curves show that elastic strain energy and kinetic energy were converted to heat during the simulation. However, the total energy always maintained unchanged, which indicates the conservation of energy in the discrete element system.