Every single particle is simulated by a polygon discrete element to capture the realistic shape of rockfill materials. A polygon discrete element method (PDEM) is developed by adopting a simple contact detection program and a polygon/polygon contact model. A linear program is adopted to detect the contact details between polygons. Then the normal contact force is calculated by a potential energy based polygon/polygon normal contact model, and a polygon discrete element calculation method is formed. Based on this method, a program called PDEM is developed to study the interaction between particles and both the translational and rotational motion of every particle from the microscopic view. The effect of micro-properties (e.g. particle shape, size, material properties et al.) on the macro-strength and deformation is enabled. A two-dimensional model test of a coarse aggregate was carried out by PDEM program. The stress and deformation laws consistent with the lab experiment were obtained, and the method and procedure were used to study the effectiveness of the rockfill.