Coordinating and Synergetic development are highlighted in guidelines and principles in the Outline of construction planning of Chengdu-Chongqing twin-city economic circle. Differences of Urban output per capita are calculated by Gini coefficient approach and then synergy degrees are measured through synergetic model based on entropy theory. The Gini coefficients appeared normal in recent years yet in a trend of rising from year of 2011 to 2019，while the degree of synergy ascended slowly and unstably，which were expected to describe the synergetic development of the city group in the twin mega polis area of Chengdu-Chongqing. City Jianyang and City Ya’an were the two main factors causing the un-synergetic development. Some ‘mutation’ would be expected to occur in the future measurement on the degree of economic synergetic development，which is referred and compared by the calculation of the degree of synergy in the Shanghai-Jiangsu urban agglomeration. The administrators of Chengdu-Chongqing urban agglomeration are expected to uphold the concept and principle of inter-city cooperation over competition，to promote resources and all the productive factors to break through administrative boundaries，aiming to speed up their free flow and accelerate the process of regional economic integration.