Technological developments in the field of construction today increasingly developed, structures built not only irregular but also irregular. Story of the irregular-structure building significantly shaped affect the building collapse. The collapse of this building can be a collapse of natural and artificial collapse. The natural collapse was a collapse caused by the load capacity received by building or exceeds the capabilities of the structure itself. The potential of structural failure due to their natural collapse can lead to progressive collapse. This research aimed to analyse the influence of flat slab against progressive collapse at irregular building structures, and determine the type of collapse that occurred at irregular building structures. This research was conducted by analysing the structural elements of the first destroyed by the addition of the maximum load. The analysis is done by eliminating one or more of the critical column based on the General Service Administration (GSA). Examination of the power structures using finite element based software, based on the value Demand Capacity Ratio (DCR). Irregular building structures undergo a progressive collapse if the value of DCR> 1. The analysis showed a progressive collapse does not occur at irregular building structures, due to the building using structural elements in the form of a flat slab. The collapse happened only on some elements of the building structure, does not occur in the whole structure of the building.