Abstract: Under the new development pattern,the “double circulation” is the active choice for China's reform and opening-up to promote each other in the new stage of development.The main reason lies in the fact that the internal conditions of China's economy have undergone fundamental changes,and it has the objective conditions to start and smooth the great domestic cycle.Its internal logic lies in the productivity screening effect and learning effect caused by opening competition,and in the regional comparative advantage and new international competitive advantage brought by institutional innovation.The relationship between the opening to the outside world and the formation of a unified domestic market is not a simple linear one,but with the increasing degree of opening to the outside world,it shows a trend of decreasing first and then increasing -- that is,at the present stage,excessive reliance on opening to the outside world will aggravate the segmentation of the domestic market and hinder the smooth flow of domestic economy. Under the background of “double circulation”,the coastal areas and the domestic regions along the “One Belt and One Road” should expand the export scale,adjust the import structure,adopt the substitute elements circulating in the domestic market,and promote the “internal circulation” by “external circulation”,which will be conducive to promoting the unification of the domestic market.

Key words: double circulation, the new development pattern, opening to the outside world, market segmentation