17 sustainable development goals (SDGs) were committed by 193 countries in 2015. Assessing the spatio-temporal progress of achieving the SDGs can help to track the global sustainable development progress and identify critical development issues to eventually accelerate the achievement of SDGs. However, there is a lack of methods for the quantitative assessment of the progress of achieving SDGs at the regional level (above the national level), especially systematic methods that can simultaneously assess regions along the “Belt and Road”. To fill this research gap, after classifying 17 SDGs into four dimensions (society, economy, environment, means of implementation and cooperation), we have developed the Composite SDG Index to represent the comprehensive performance of achieving SDGs. Specifically, the index is constructed by two sub-indices, including the SDG subindex used to assess the overall performance of achieving the four dimensional SDGs and the Coupling Coordinated SDG subindex used for the first time in the SDG assessment to measure the coupling coordination degree between the four SDG dimensions. To implement this methodological framework, we chose 15 countries along the “Belt and Road” as the case study, and used 108 indicators to assess the performance of achieving SDGs for these countries. Eventually, various national development models and related policy recommendations were proposed. The three indices included in the methodological framework developed in this study can effectively enhance the global stakeholders' mutual understanding of the progress of achieving SDGs to support regional coordinated planning and national-level strategic decision-making. Display omitted •A composite method for assessing regional progress of achieving SDGs was successfully constructed and testified.•The coupling coordinated index was also constructed and used for the first time in the SDG assessment.•For the sample region, countries belonging to the Central and Eastern Europe had the best progress of achieving SDGs.•Three national development models and related policy recommendations were proposed.