Due to the increasing health care organizations costs, their requirement to increase the quality, and also the complexity of their systems, the issue of the change and improvement to the systems has got really important. It was crucial to know which of methods and scenarios for the change of the systems, especially in the resources, lead to better conditions and this topic caused major issues. In this regard, discrete – event simulation as one of the decision making tools in operations research based on random data, has significantly helped policy makers and a managers. In this study, firstly, the key performance measures of Ghaem hospital emergency system using past publications and experts’ suggestions were identified. Then this system was modeled and simulated using Arena software. After weighting the criteria by AHP method, the scenarios of the experts were defined. Finally they were ranked using PROMETHEE method and the most suitable scenario was determined.