Abstract: Non-grain conversion of cultivated land is an important factor threatening national food security. Based on panel data from 13 major grain-producing provinces in China from 2011 to 2024, this paper employed Moran’s I, kernel density estimation, and the spatial Durbin model (SDM) to reveal the characteristics and spatial spillover effects of non-grain conversion of cultivated land from three dimensions: temporal evolution, spatial pattern, and driving factor. The results revealed that: (1) Temporally, the average non-grain conversion rate of cultivated land in major production areas generally showed a trend of first declining and then rising, standing at 26.0% in 2011 and 25.6% in 2024, with inter-provincial divergence continuing to intensify, as the standard deviation increased from 10.64 to 12.69. (2) Spatially, the non-grain conversion rate of cultivated land exhibited significant positive spatial agglomeration (mean Moran’s I = 0.644), generally manifesting a pattern of “high in the south and low in the north, with bipolar agglomeration”, in which Hubei and Hunan formed the stable high-high agglomeration core, while northeastern provinces such as Jilin formed the low-low agglomeration core; kernel density estimation further revealed a “dual-track” differentiation characterized by convergence and decline in the north and divergence and increase in the south. (3) Regarding driving factors, per capita GDP and the intensity of fiscal support for agriculture pushed up the non-grain conversion of cultivated land in neighboring provinces through spatial spillovers, urbanization and agricultural mechanization produced inhibitory spillovers, and the effective irrigation rate primarily suppressed non-grain conversion in the province itself through direct effects. Accordingly, policy recommendations are proposed, including differentiated regional regulation, enhanced comparative returns for grain production, and establishing an inter-provincial collaborative governance mechanism.