The overcrowding situation in emergency department is serious problem worldwide. In fact, the majority of developing countries are interested in developing their hospital system in order to anticipate the overcrowding situations and ameliorate the quality of patient care. In this paper, we focus on patient pathway in an Adult Emergency Departments (AED). This process presents the main burden for overall system operation due to its growing dynamics and the distributed organizational structure of hospitals. In order to determine the key performance indicators for the internal functioning of AED, we are building a workflow model based on the real patient pathway to direct the patients into the dedicated service while respecting the quality of care according to the expectations and requirements of the patient. Our approach is tested on a set of real database from AED of CHRU in Lille (France). Simulation results show that the proposed model can determine 3 keys performances indicators to optimize in order to improve the patient pathway in the AED.