The relative young functional modeling approach is becoming a promising and leading technique in these areas of risk assessment and reliability engineering. This paper proposed a universal graphical interface tool, Multilevel Flow Models Studio (MFMS), for Multilevel Flow Models (MFM) based modeling and application development. An Extensible Markup Language based file structure is introduced to represent the MFM model for the target system. With a friendly graphical interface, MFMS mainly consists of two components: an editor to intelligently assist user establish and maintain the MFM model; and an executor to implement the application for various purposes in terms of the established MFM model. A prototype MFMS system has been developed and applied to construct a demonstration/evaluation system for the deregulated Natural Gas industry of Japan.