Abstract: A systematic method for analyzing load trajectory deflections of nuclear ring cranes was presented, including the governing equations of equilibrium paths and their compatibility conditions. Properties and formulations of the variables involved in these equations were studied in detail, in which the variation in pull directions of ropes with positions of pulleys was taken into account and a numerical method was derived to ensure the roping manner conforming to the common tangent of two pulleys. Moreover, we also provided a method to compute rope lengths wound by the drum and between two out rope points on pulleys, and the transitive relation for rope velocities between two ends of the pulley was derived. To a large extent the proposed method is universal and can be applied to general rope-pulley systems.