Abstract: Conservation tillage is an environment-friendly agricultural cultivation technique that distinguishes itself from traditional tillage, and its implementation relies on agricultural machinery. China’s unique situation as a large country with many small-scale farms has led to the development of a distinctive path for agricultural machinery in the form of cross-regional agricultural machinery services. Therefore, it is worth exploring whether conservation tillage machinery drives the spatial spillover of the net carbon sink of conservation tillage in the context of cross-regional agricultural machinery services. This study used panel data from 30 provinces in China (excluding Hong Kong, Macao, Taiwan, and Tibet) from 2000 to 2020. First, an exploratory spatial data analysis was used to reveal the spatial agglomeration characteristics of conservation tillage machinery and its net carbon sink. Second, the spatial spillover effect of conservation tillage machinery on net carbon sink was quantitatively analyzed using the spatial Durbin model. Furthermore, this study analyzed the heterogeneity of the spatial spillover effect of conservation tillage machinery on its net carbon sink from the dimensions of time, topography, and major grain-producing areas. The study found that: 1) from 2000 to 2020, mechanical power and the net carbon sink of conservation tillage increased from 22.55 million kW and 7.93 million t C in 2000 to 238.63 million kW and 33.17 million t C in 2020, with average annual growth rates of 12.52% and 7.42%, respectively. The growth trends were significant, and their development was closely synchronized. The spatial correlation results indicated that both of them mainly exhibited regional agglomeration characteristics with “high-high” and “low-low”, showing a significant positive spatial correlation. 2) In the context of cross-regional agricultural machinery services, conservation tillage mechanical power significantly drove the spatial spillover effect of net carbon sink of conservation tillage. This manifested as a positive spatial spillover effect of the mechanical power of conservation tillage on the corresponding net carbon sink in neighboring provinces. Specifically, straw-returning mechanical power exhibited a positive spatial spillover effect, whereas no-tillage mechanical power, owing to its long-term implementation, mainly showed a negative spatial spillover effect, which can lead to crop yield reduction. 3) The spatial spillover effect of conservation tillage mechanical power on the corresponding net carbon sink exhibited heterogeneity across different time periods, topographies, and major grain-producing areas. In the temporal dimension, the spatial spillover effect was significantly positive and increased during the 2004–2009 and 2010–2013 periods. In the topographic dimension, the spatial spillover effect was positive in plain areas but negative in hilly and mountainous regions. Among the major grain-producing areas, the spatial spillover effect of conservation tillage mechanical power on the corresponding net carbon sink was more pronounced in rice-producing areas. The spatial spillover effect of no-tillage mechanical power was relatively prominent in the wheat-producing areas. The spatial spillover effect of the straw-returning mechanical power was essentially the same across the three major grain-producing areas. This study proposes measures to promote conservation tillage, establish an agricultural machinery service information platform, and enhance the level of conservation tillage of agricultural machinery and equipment. Additionally, the research findings hold significant reference value for how the government can use conservation tillage to contribute to the dual-carbon target.