This study refers to a result of the study of the causality between agricultural mechanisation and grain production. It applied data from 280 prefecture-level cities across China from 2000 to 2018 with the SPDM model. This paper concludes that (1) when other conditions remain unchanged, the improvement of the level of agricultural mechanisation will not only significantly increase the local grain output but also have a noticeable spatial spill-over effect on the grain output of other regions through the cross-regional operation of agricultural machinery; (2) in the long run, the spatial spillover effect of agricultural mechanisation on grain production is greater and more evident than the direct effect; (3) the spatial spillover effect of agricultural mechanisation on grain production decreases with the increase of cross-regional distance.