at last, some conclusion has been obtained . at present the effect of cable and its pre-stress is not very clear . based on the rule of conversation of energy, it is proved to be right in theory that the stiffness of the linear elastic structure is larger with the increase of its pre-stress 针对目前关于索在结构中的作用以及索中预应力的增加对结构刚度的影响到底如何等讨论,本文从能量守恒原理出发,从理论上推导证明了在线弹性范围内,结构的刚度随预应力的加大而提高这一重要结论。