Applications of formal methods to critical systems such as railway systems have been studied by several research works. Their ultimate goal is to increase confidence and to ensure the behavior correctness of these systems. In this paper, we propose to use the Event-B formal method. As a central concept in Event-B, refinement is used to progressively introduce the details of systems requirements, but in most cases, it leads to voluminous and complex models. For this purpose, this paper focuses on decomposition techniques in order to manage the complexity issue in Event-B modeling. It presents a state of the art and an analysis of existing decomposition techniques. Then, an approach will be proposed following this analysis.