An analysis process for break impact loadings to tower, conductors and unfaulted insulators is proposed when one of the composite multi- insulators tension string comes to rupture. A finite element method is used to simulate the break impact process in order to consider the whole structural model of transmission lines and geometric nonlinearity. And a two-step calculation process, form-finding analysis and break impact analysis, is performed. The calculation results are verified by testing data. And an impact influence coefficient is defined to characterize the influence of maximum impact loading to tower, unfaulted insulators, conductors and fittings. A typical example with the structure of three-composite-insulators string and two/three suspension points is presented. The impact loading characteristics are obtained with different fracture locations. The obtained results are beneficial to design composite multi-insulators tension string structure.