Presented in this study is a top-down functional modeling procedure and the desired functionalities of energy management system (EMS). For the purpose of top-down modeling for EMS, energy management system is categorized into 7 subsystems based on common functionalities and energy management life cycle. After that, benchmarking analysis of commercially major EMS products is conducted. As a result of this analysis, desired functionalities of each subsystem of EMS are suggested in this study. This study is served as a useful guidance about essential functional requirements of energy management system to the practitioners involved in the development or introduction of EMS.