From the point of view of systems science and the theories of self-organization, the author reveals that "sustainable development" is the order parameter of the social economy system as the proceeding of its development and evolution, possesses all the properties of order parameter and governs the further development of the social economy system as well. The synergetic mechanism and effect in regional composite system's sustainable development is analyzed and the conceptual model of synergetic management is raised and created. It is revealed that the synergetic management has the important role in sustainable development of a regional composite system.