Abstract: Promoting the upward flow of agricultural products is a key measure for stimulating industrial vitality in county-level economies and holds significant implications for their sustained growth. This paper treated the implementation of the “Internet+” Agricultural Products from Rural to Urban Areas Program as a quasi-natural experiment for agricultural product upstreaming, and constructed a difference-in-differences model based on balanced panel data from 1 796 counties in China spanning from 2010 to 2023 to identify the causal effect of this policy on county-level economic growth. The findings indicated that the implementation of the agricultural product upstreaming policy significantly promoted county-level economic growth, and this effect remained robust across a series of robustness checks. Mechanism analysis revealed that attracting industrial and commercial capital inflows, facilitating industrial upgrading, and stimulating consumption vitality were important channels through which the policy generated its growth effects. Further analysis showed that the policy exhibited positive spatial spillover effects, contributing to coordinated regional economic growth. This paper confirmed the economic growth effects of agricultural products upstreaming policy implementation, offering certain insights for the refinement of subsequent agricultural product upstreaming policies and the high-quality development of county-level economies.