Rockfall is a frequent engineering disaster confronted in the capital construction engineering. The key for preventing rock fall is the evaluation of the rockfall trajectory. After extensive analysis, an innovative calculation method of rockfall trajectory, called segmented cycling algorithm, has been proposed in the paper. According to the contact relationship between the rolling stones and the slope surface, the movement divided into three sections which include the jumping phase, the rolling (sliding) phase and collision phase, the formulae to calculate the velocity of different phases of motion are proposed respectively by segmented cycling algorithm. A similar model, based on a rock slope in Chongqing-Wanzhou highway, is established to verify the capability and validity of the presented algorithm. Compared with existing algorithm, the new algorithm is simple and clear, easy to use and so on. The algorithm meets the law of the movement of rockfall and can be used to forecast the kinetic feature of rockfall. It is also used as the basis for rockfall disaster prevention.