The presence of a large number of loose rocks, often accompanied by giant rocks, which are highly destructive to the surface are an important factor in geological hazard risk assessment. In rocks moving along a slope, the scale of movement and the scale of deformation differ substantially in magnitude owing to their movement characteristics of large moving distance, fast rotation speed, and small deformation. A multilevel model for rock motion calculation is established to separate the rigid displacement and deformation displacement of the rock. The total rock movement displacement comprises translational displacement, rotational displacement, and deformation displacement. Three corresponding coordinate systems are set up. These include the translational coordinate system, which is used to describe the translational displacement of the rock, the rotational coordinate system, which is used to describe the rotational displacement of the rock, and the co-rotational coordinate system, which is used to describe the deformation displacement of the rock. The origin and the direction of the coordinate axis of the co-rotational coordinate system change with the movement of the rock. Lagrange’s principle establishes the equations of motion, which is solved by an explicit approach in the framework of the Continuum-discontiuum element method. Several numerical cases verify that this method can accurately calculate the rotational movement of the rock.