General aspects regarding software quality are discussed. Bayesian networks mathematical model is proposed to evaluate the software quality, from the reliability point of view. This model was previously used to evaluate a substation monitoring software system developed in Romania as case study. Currently, we extend it to evaluate the reliability of a software system for EMS (Energy Management Systems) and DMS (Distribution Management System) software systems. These systems include substation monitoring software systems and are seen as the core of any national energy system as they are used the National Dispatch Control Center. A simulation is performed to obtain some practical results and draw important conclusions if this model can improve the EMS and DMS software systems.