FinTech emerges as an instrument in a rapidly evolving world, offering innovative solutions to mitigate natural resource constraints, and thus achieve sustainable development. However, its influence remains unclear. To clarify this effect, this study aims to explore the sustainable development effect of FinTech In the context of natural resource constraints. Firstly, this paper empirically examines the sustainable development effect of FinTech using a two-way fixed effects model based on data from 270 Chinese cities from 2006 to 2021. Secondly, this paper delves into the moderating mechanism behind the sustainable development effect of FinTech by assessing the level of marketization and the progress of green technology. It reports three key findings: (1) FinTech significantly impacts sustainable development, following a distinctive U-shaped pattern, thus contributing to alleviating resource constraints. (2) Heterogeneity analyses show that this U-shaped relationship is more pronounced in the central and western regions, as well as in regions with a higher degree of development in the level of fintech. (3) Marketization and green technology influence the U-shaped relationship between FinTech and sustainable development, shifting it upward and to the left. These findings recommend practical policy suggestions for local government.