With the building of sustainable cities being listed as one of the Sustainable Development Goals in the 2030 Agenda, cities in developing countries are facing more severe challenges. Therefore, it has become very urgent to evaluate and compare sustainability under different policy intervention scenarios. Based on the principle of system dynamics, this study constructed an urban sustainability evaluation model covering six subsystems: economy, livelihood, risk, environment, pollution governance, and resource. Using 13 cities in the Beijing-Tianjin-Hebei region as study cases, 5 future policy scenarios were designed under the framework of the Shared Socioeconomic Pathways to simulate the variation of the urban sustainability index in each city by 2035. The results reveal that: (1) Medium and small-sized cities around Beijing are facing more challenges to achieve sustainable urban development; (2) the urban sustainability index in each city varies under different policy scenarios. (3) the gap of urban sustainability in the Beijing-Tianjin-Hebei region does not show a significant narrowing trend and is likely to widen in the future. The approach can also be applied to other regions to provide decision support for choosing urban development pathways after comparing possible future trajectories of sustainable urban development.