Disaster degree and hazard risk of rockfall is essential for roadside slope design for safety. This paper is concerned with research efforts to calculate full motion trace of the rockfall along road slope with effective and numerical analysis methods. Two main terms including gradient of side slope and damping function between rockfall, mountain slope and rock speed are employed in so-called Damping and Rebounding Osculation Method (DROM). This tool is developed to define rock motion trace and delve into motion characteristics such as direction and rotational angle speed of the rockfall. Hereon, polygon rock is regarded as a rigid body of Non-particle and the motion formula are set up with the revolution motion of rock rigidity. The objective of this study is to accurately characterize the rockfall motion trace for disaster prevention and mitigation.