Belt and Road Initiative (BRI) economies are rapidly expanding infrastructure, tourism, and investment connectivity, yet these developments may also increase energy demand and carbon emissions. This study assesses the environmental impact of Chinese outward foreign direct investment (FDI), tourism growth, and technological advancement on carbon emissions in 60 BRI countries during 2000–2024. The study contributes by examining Chinese outward FDI rather than aggregate FDI, incorporating the interaction between Chinese outward FDI and tourism development, and comparing environmental effects across major BRI regions. Using the Cross-Sectionally Augmented Autoregressive Distributed Lag (CS-ARDL) approach, supported by Common Correlated Effects Mean Group robustness estimates and Dumitrescu–Hurlin causality analysis, the results show that Chinese outward FDI and technological innovation reduce carbon emissions in the full BRI sample over the long run. In contrast, tourism development, industrial value added, and the interaction between Chinese outward FDI and tourism development increase carbon emissions, indicating that tourism-intensive and infrastructure-led development can intensify environmental pressure. The regional results reveal that Chinese outward FDI increases emissions in South Asia and the MENA, whereas it reduces emissions in Southeast Asia, Central Asia, Central and Eastern Europe, Western Europe, and the Commonwealth of Independent States countries. The findings also support the Environmental Kuznets Curve hypothesis in the full sample and regional subsamples. The results highlight the need to direct Chinese investment toward renewable energy, clean transport, and energy-efficient infrastructure; embed low-carbon standards in tourism mobility and accommodation; accelerate technological upgrading; and adopt region-specific industrial and environmental policies. This study advances understanding of how Chinese outward FDI, tourism growth, and technological advancement jointly shape environmental sustainability across BRI economies.