Controlling fertilizer nonpoint source pollution is the key to promoting sustainable development of agriculture, and farmland circulation is an important part of the rural farmland system reform. Clarifying the relationship between land circulation and fertilizer nonpoint source pollution can provide reference for the realization of agricultural green transformation goal. Based on a panel data of 30 provinces from 2005 to 2022, and applying the fixed effect model and spatial Durbin model, this paper tested the impacts of farmland circulation on fertilizer nonpoint source pollution intensity and its spatial spillover effects, and examined the spatial action mechanism by the mediating effect model. Results show that: 1) farmland circulation has a significant inhibitory effect on fertilizer nonpoint source pollution intensity; 2) there is a significant negative spatial spillover effect of farmland circulation on fertilizer nonpoint source pollution intensity, and this effect shows spatial attenuation characteristics with the increase of geographic distance; and 3) the spatial spillover effect is mainly realized through the demonstration effect and the regional competition effect. Based on the above conclusions, this paper suggests: constructing regional green demonstration sites, optimizing policy incentive mechanisms, and deepening the cross-regional collaboration networks.