Interregional capital mobility is crucial for high-quality development. Existing literature highlights the role of geographical and boundary effects on interregional investment, but often overlooks cultural differences. Using administrative records of business registration data covering nearly 200 million firms in mainland China from 2005 to 2022, we construct a novel panel data on interregional investment networks and reveal that surname distance as a metric of cultural differences significantly inhibits interregional investment, with elasticities of −0.955 and −0.713 on the amount and quantity, respectively. Furthermore, the mechanism analysis demonstrates that increased surname distance heightens survival risks, shortens market duration, and leads to more litigation for firms investing in culturally distant regions. This impact intensifies over time, is more significant in regions with low marketization levels, and has a pronounced effect on intraprovincial investments.