In order to study progressive-collapse resistance robustness of a frame structure, we propose a quantitative analysis method of structural robustness, based on the mechanical characteristics of the frame structure under an earthquake. We verified the correctness and practicability of this method with an example. The results showed that the quality of structural robustness was relative and negatively correlated with the load magnitude. The quantitative analysis method of structural robustness can be used for the structural design scheme selection. The structural robustness can be improved by reducing the member vulnerability coefficient of important columns, protecting the component with a large vulnerability coefficient and importance coefficient, strengthening the connection between members, and ensuring the reliability of the load path under extreme conditions.