This paper explores the impact of big data infrastructure development on banks' Fintech innovation. Analyzing data from 1882 bank-year observations of 297 banks between 2011 and 2021, we find that the National Big Data Comprehensive Experimental Zones significantly enhance banks' Fintech innovation. Our results indicate that data element agglomeration is the channel that influences banks' Fintech innovation. Further analyses show that big data infrastructure development more effectively promotes Fintech innovation in banks with larger scale, lower loan concentration and credit risk. These findings contribute to the existing literature by identifying the determinants of banks' Fintech innovation in the digital era.