Abstract：Consideration of structural robustness is one of the most important measures to guarantee the structural safety，especially to deal with unexpected events. How to evaluate the structural robustness quantitatively is one of the most challenging problems in structural engineering. A new method to calculate the importance coefficient of components in structural robustness evaluation is given，which focuses on the change of structure capacity after removing a certain component in the structure. From conception，the structural topological relation，the component stiffness and strength，and the effect of external loads are all considered synthetically. Besides，from mechanics，how the broken component influences the remnant structure are also described，which can be used to explain the physical meaning of the new coefficients. At the same time，from global point of view，the interaction between the structural property and the external load effects is considered. The loading process is completed until the structure becomes a mechanism，to some extent，which helps to establish the relationship between component importance and structural robustness. From algorithm，a method called perturbation is used. It bridges the structural stiffness matrix before removing some component with that after removing，by which the rearrangement and inversion of the structural stiffness matrix can be avoided. Instead，the dimension of the structural stiffness matrix in each stage is only decided by the number of the broken components. The inversion calculation is easy，which only needs to treat some specific large sparse matrices. Finally，as practical examples，two plane trusses are given. Comparing with some existing indexes of component importance，the internal relations between them are found，and the correctness and rationality are also proven.
