This paper selects 1301 county-level data in China from 2011 to 2019 to study the impact of rural financial digital development on agricultural economic growth, and uses the dynamic panel PTR model to identify the “digital threshold effect” of agricultural economic growth. The main conclusions are as follows: First, the popularization of rural financial digitization can significantly boost agricultural economic growth, mainly because digitization improves financial availability in rural areas. Further mechanism analysis shows that this impact is mainly due to the width of digital coverage. As limited to the inherent characteristics of rural areas, increasing the depth and complexity of digitalization is not conducive to stimulating agricultural economic growth. Secondly, agricultural economic growth has an obvious “digital financial threshold effect”. Specifically, when the digital financial index exceeds 234.39, the impact of financial development on agricultural economic growth will change from a single “financial availability promoting growth” to a “synergy of availability and scale improvement promoting growth”. Finally, most regions in China have now exceeded the “digital financial threshold”. This means that financial digitalization has brought new opportunities and new changes to the development of China’s agricultural economy.