The coordination of economy, energy, and environment plays an important role for cities seeking green transformation and sustainable development. However, poor information and equivocal data are what often face the related analysis. In this paper, the correlation and synergy of the urban economy-energy-environment system are analyzed. First, the Grey relational analysis and entropy weight method are combined and introduced to analyze the correlation degree in the indicator level and the subsystem level of the 3E system. Then, the concepts of ordinal parameter and comprehensive correlation degree are introduced, to evaluate the ordering degree of subsystems and the synergy degree of compound systems. Finally, the data of Beijing from 2008 to 2017 are used for empirical study. Results suggest that a fluctuating tendency of low synergy or none synergy is observed in the Beijing 3E system. Furthermore, the improvement of the energy subsystem displays dominant effects on the coordinated development of compound systems, and the technological innovation andThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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Paper‐based composite packages, which have been widely used for beverage in modern daily life, are featured of nutrition preservation and convenience. However, it is also causing environmental problems in urban areas because of the low recycling rate. The introduction of extended producer responsibility (EPR) is helpful to improving the recycling rate of beverage paper‐based composite packaging by extending the producer's environmental‐protecting responsibility for the product from its production to its end‐of‐life treatment. To find out the optimal strategy of applying the EPR system for beverage paper‐based composite packaging, this paper is conducted based on the basic framework of the EPR system, combined with the specific requirements of the EPR System Implementation Plan promulgated by China and the Implementation Plan of the EPR System for Beverage Paper‐Based Composite Packaging. An evaluation index system for beverage paper‐based composite packaging manufacturers is constructed to perform the EPR system, including three management‐level indicators, 10 standard‐level indicators and 42 programme‐level indicators. A comprehensive evaluation method is introduced to help the producers to fulfill the extended producer responsibility. Results suggest that beverage paper‐based composite packaging producers should first fulfill the responsibility in information disclosure, ecological design and use of recycled materials.