Abstract: Beijing Tianjin Hebei (Jingjinji) forms a typical and important regional ecosystem.The basic feature of regional ecosystem is symbiosis.The synergic development of Jingjinji involves economy，ecology and society，of which economic synergy is leading，eco synergy is the basis，and social synergy is the aim.The key is to develop and construct the symbiosis mechanism and mode of regional ecosystem in Jingjinji.Since its synergic development is the state strategy，it requires following symbiosis law，basing on mutualism，making a scientific clarification of responsibility，rights and benefits of the three sub regions，and carrying out operable measures.Besides，it also demands a proper planning on the top level，a proper strategic disposition so as to push forward the economic development and social prosperity of the region based on eco symbiosis.

Key words: Jingjinji synergic development, complex ecosystem, symbiosis mode, symbiosis mechanism