Carried out studies on space structures signify the momentous influence of imperfections on the load bearing capacity of these structures. Many of these imperfections such as initial curvature in members are all innately random and can affect the bearing capacity of the members and consequently that of the structure. In this paper, the effects of the probabilistic distribution of initial curvature on the bearing capacity of flat double layer grid space structures with different pattern have been studied. 8 flat double layer space structures with different pattern were selected and 8000 nonlinear finite element analyses were done. At first, based on the random initial curvature imperfection amount of the member, the material property was updated. Afterwards, based on the push down analysis, the ultimate load bearing capacity of the structure was determined through nonlinear analyzes performed by the OpenSees software and this procedure was repeated numerous times. Finally, based on the Monte Carlo simulation method, the structure’s reliability diagrams were procured. The acquired results signify the sensitivity of the behavior of flat double-layer space grids to the random distribution of initial imperfections.