Abstract: Integration of Jing-Jin-Ji Region has long been interpreted as the integration of market, public service, environmental protection and ecological civilization construction as well as local plan, while the integration of legal system has been somehow neglected. The integration of legal system is the guarantee for the economic and social development of Jing-Jin-Ji Region. It shall be hard for Jing-Jin-Ji Region to keep a sustainable development without the integration of legal system. The integration of legal system of Jing-Jin-Ji Region may be achieved either through regional legislation by a regional legislative body to be set up or through synergistic legislation by different legislative bodies in this region, and currently the latter seems to be more practical, considering the reality of our legal system and other facts. Synergistic legislation may resolve the problems caused by the inconsistency of rules in the three places, therefore, shall be taken as the main path for the integration of legal system of Jing-Jin-Ji Region. Since synergistic legislation in nature is the cooperation among local legislative bodies, lacking of binding, and therefore has its limitations. To maximize the role of synergistic legislation, the three places in this region are expected to share legislative information, clarify the principles and focus of synergistic legislation, examine timely the effects of the synergistic legislation, in order to establish modes and mechanisms of synergistic legislation suitable for the development of this region.