It is important to estimate the trajectory and motion behaviors of falling rocks in rockfall preventive measures such as rockfall hazard and risk assessment, design and performance evaluation of rockfall protection structures. The trajectories of falling rocks can be described as combinations of four types of motion: free fall, rolling, sliding and bouncing of a falling block. This study shows that these four basic types of motion can be simulated by DDA with high accuracy. A close comparison is carried out on motion behaviors between 2D and 3D DDA simulation. The merits and nota bene in the application of DDA are explored in this paper.