Based on previous research, an innovative method to investigate object dynamics is suggested. Concerning DEM itself, it can precisely simulate the interaction among discrete spheres. DEM is a powerful tool in simulation and calculation. One sphere is kinetic in an inclined plane with 45°. After reasoning theoretical formula and establishing theoretical model by which theoretical relations between velocity-time and displacement-time are acquired respectively, DEM is employed and visual sphere-inclined plane is archived in the platform of Borland C++ 6.0, then, the theoretical formula is deduced. and the theoretical curves are drawn. Also, critical coefficient of friction will be determined when sphere is purely rolling in an inclined plane. The relationship of velocity-time and displacement-time will be achieved respectively when sphere moves on pure displacement condition, sliding and rolling condition, and purely rolling condition, then their relational curves are drawn. These curves are compared to theoretical curves of the relationship between velocity-time, and the relationship between displacement-time. It is concluded that computed results and theoretical results are consistent. Therefore, it is verified that theory of DEM is available.