Selecting the relevant data from 2012 to 2021, the economic collaborative development level of each subsystem of Shenyang Modern Metropolitan Area, Liaoning Coastal Economic Belt, and the composite system of "One Area and One Belt" of Shenyang and Dalian was analyzed by measuring the economic correlation degree, order degree and synergy degree of cities. The results show that the economic connection intensity between Shenyang and its peripheral cities is relatively strong, while that of Dalian and its peripheral cities is relatively weak. The order degrees of each subsystem of Shenyang Modern Metropolitan Area and Liaoning Coastal Economic Belt both show a decreasing and increasing process, and the orderliness is developing continuously for the better. The synergy degree of the composite system of "One Area and One Belt" of Shenyang and Dalian is in a good synergy state, but there is still room for improvement. In the future, it is necessary to start from strengthening the radiation and driving effect of core cities, improving the orderliness of the development of each subsystem, promoting the linkage development of "One Area and One Belt" of Shenyang and Dalian, and optimizing the overall design, to improve the regional economic collaborative development level of Liaoning Province.