Abstract: The Steel-frame structure is widely used in engineering construction due to its main merits of rapid construction speed,excellent performances of ductility and light quality,etc.However,the capability of resistant incentive progressive collapse under explosion and the progressive collapse mechanics of the steel-frame structure is not clearly addressed up to the present.Aiming at this issue,this study conducted a simulation analysis of progressive collapse under explosion by employing numerical simulation method and combining GSA criteria,based on a four-story steel-frame model which was designed by the specifications of Chinese code.Therefor,a complete series of numerical calculating methods on progressive collapse under explosion was established.By adopting this series of methods,the progressive collapse mechanism,structural members failure modes and forced states were studied and presented in this paper.The outcome showed that this series provided with accuracy,reliability and applicability.Moreover,through the study,the results indicate: in the process of structural collapse after some partial components are damaged,failure modes of collapse forms and components are greatly affected by catenary mechanism;catenary tension directly or indirectly results in local warping and plastic instability of structural members.