Abstract: At present, environmental problems are becoming increasingly severe, and sustainable development concerns the common destiny of all mankind around the world. Leveraging ecological footprint and ecological carrying capacity data for Eurasia from 2000 to 2022, this study employs a three-dimensional ecological footprint model to conduct a multi-scale sustainability assessment. Further applying a difference-in-differences model, we analyze the impact mechanisms of the Belt and Road Initiative on Eurasia's ecological footprint. Quantile regression and heterogeneity analysis reveal Belt and Road Initiative's differential effects across countries. Key findings indicate that: (1) Eurasia's unsustainable development intensified from 2000 to 2022, with ecological footprint depth rising from 1.966 to 2.513 ha/cap, while per capita ecological footprint size declined slightly from 1.092 to 1.023 ha/cap. (2) Classifying 83 countries into 9 sustainability types based on ecological footprint depth and size, Asia showed weak sustainability (low size-medium depth and low size-low depth types), while Europe was primarily low size-medium depth with relatively stronger sustainability. Six countries experienced weakened sustainability and six improved. (3) The Belt and Road Initiative significantly increased ecological footprint in Eurasian countries, mediated by industrial structure, technological innovation, and foreign direct investment. Quantile regression indicates Belt and Road Initiative's effect is stronger in nations with lower initial ecological footprint. Heterogeneity analysis further shows Belt and Road Initiative disproportionately impacts countries with lower ecological footprint depth, smaller per capita ecological footprint size, and weaker sustainability. These insights provide critical guidance for implementing the UN 2030 Agenda and formulating Belt and Road Initiative policies to enhance long-term sustainability.