This paper provided a practical method to decide the reasonable spoke cable pre-stress for flexible Ferris wheels. By analyzing the factors influencing spoke cable pre-stress, this paper proposed a method to determine pre-stress value range and a method to adjust the value range, pointing out that the lower limit is determined by the slack of the 0 degree cable, and the upper limit is controlled by the safety factor of the spoke cable. The reduction of wheel weight and spoke cable safety factor can both expand value range, but the increase of spoke cable section area may cause a vicious cycle in spoke cable pre-stress adjustment. Other factors affecting spoke cable pre-stress, including wheel rigidity and cable sag, were also analyzed. Besides, since the mechanical property of flexible Ferris wheels can be generally decided by the ratio R of spoke cable pre-stress and wheel weight, flexible Ferris wheels of different scales can take similar R value as Beijing Great Wheel to decide an approximate pre-stress value.