In order to solve the safety evaluation problem of existing prestressed cable truss structures considering the corrosion degree of cables, an objective evaluation system is established based on the characteristics of the structure and the corrosion degree of the cables. Firstly, the dynamic response analysis method of cable-strut system under the instantaneous break is established, and the rationality and feasibility of proposed method are verified by three cable structures. According to the construction theory of judgment matrix and the result of the cable breaking analysis, the method for determining the weight coefficient of each cable in the cable-strut system is established considering the corrosion degree of the cable. On this basis, the membership function of the corrosion degree of the cable is established, and the safety evaluation set of the cable system is built. At last, based on the weight coefficient and the corrosion degree of the cable, the fuzzy comprehensive evaluation system is established for the safety of existing prestressed spatial cable system. Furthermore, the weight coefficient determination method, the membership function and the fuzzy comprehensive evaluation model are applied and verified by a practical spatial cable-strut structure.