Abstract: The development of agricultural socialized service is a crucial component in promoting the green transformation of grain production, and it represents an inevitable strategic choice to consolidate the foundation of grain security under the current circumstances. With increasing environmental constraints and the urgent need to improve production efficiency, agricultural socialized service has become an essential mechanism for modernizing agriculture and achieving sustainable development in the grain sector. In this paper, we used the super-efficiency Slack-Based Measure (SBM) model and the Global Malmquist-Luenberger (GML) index to measure the grain green total factor productivity of 30 provinces in China from 2003 to 2022, and constructed a dynamic spatial Durbin model to examine the spatial impacts of agricultural socialized service development level on the grain green total factor productivity and its regional heterogeneity. The study shows that: 1) From 2003 to 2022, China’s provincial grain green total factor productivity shows a continuous upward trend and a spatial pattern of “high in the east and low in the central and western parts of the country”; 2) China’s grain green total factor productivity and the development level of agricultural socialized service both have obvious positive spatial correlation; 3) In the short term, the improvement in the development level of agricultural socialized service not only enhances the grain green total factor productivity in the region, but also shows a significant positive spatial spillover effect. This result remains robust across a series of tests.4) The impact of agricultural socialized service development level is characterized by regional heterogeneity. In the short term, it has a significant positive spatial spillover effect on the grain green total factor productivity in the eastern region, the Main grain-producing region and the Main grain-consuming region; in the long term, only the main grain-producing region with a more solid agricultural foundation can continue to play a role in promoting agricultural socialized service and drive the neighboring areas to improve the grain green total factor productivity. 5) The degree of government intervention, the structure of agricultural cultivation, the level of urbanization, and the level of industrialization all have a significant positive effect on the green total factor productivity of food in neighboring regions. Based on these findings, it is recommended that China strengthen the coordinated governance of agricultural socialized service and green grain production transformation. Furthermore, promoting inter-regional collaboration in agricultural services and optimizing the spatial allocation of green grain production according to local conditions will be essential to advancing the sustainable development of China’s grain economy.