With the gradual northward shift of China's grain production center, the role of northern China has become increasingly crucial in food production. Understanding the spatiotemporal characteristics and driving mechanisms of cropland vegetation changes in this region is of significant importance for revealing the evolution of agricultural ecosystems, optimizing regional agricultural development strategies and ensuring national food security. In this study, northern China was divided into three subregions: Northeast, North China and Northwest. Based on the combination of GIMMS LAI3g remote sensing products, land use products, digital elevation model (DEM), climatic factors and other datasets from 1982 to 2018, this study employed the Theil-Sen median trend analysis and Mann-Kendall test to assess the spatiotemporal variations of cropland vegetation leaf area index (LAI). Furthermore, residual analysis and geographical detector model were applied to identify and quantify the relative contributions of key driving factors. The results showed that: (1) Cropland vegetation LAI in northern China exhibited a significant increasing trend from 1982 to 2018, with an average annual growth rate of 0.0064. The trend demonstrated distinct phase characteristics: the initial phase (1982—2000) was characterized by relatively slow growth, with North China showing the highest annual increase rate (0.0121), while the subsequent phase (2000—2018) witnessed accelerated development, particularly in the Northwest region, where the annual growth rate reached 0.0180, surpassing North China to become the fastest-growing area; (2) The spatial distribution of the average cropland vegetation LAI displayed a general east-high and west-low pattern, with higher values (LAI>1.5) primarily concentrated in areas with low elevations (0—500 m) and gentle slopes (0—2°). Throughout the study period, significant greening areas accounted for 57.6% of the total study region, exhibiting distinct spatiotemporal differentiation patterns. The earlier period (1982—2000) was characterized by minimal significant changes, with only localized improvements in North China, while the latter period (2000—2018) witnessed substantial expansion of significantly greened areas, particularly prominent in the Northwest region. (3) The driving mechanism analysis revealed that human activities were the dominant factors influencing the greening or browning of cropland vegetation in northern China, especially in the Northeast region, where human interventions were the most pronounced. Further analyses exhibited that agricultural machinery power, effective irrigated area, and agricultural sown area were the main driving factors influencing the cropland vegetation LAI changes in northern China. However, the relative importance of these factors exhibited distinct regional variations. Agricultural production in Northeast and North China relied more on agricultural mechanization power (q > 0.6), while irrigation was a primary factor in Northwest China (q > 0.9). These findings provide scientific basis for agricultural management in northern China, which can support sustainable development and ecological restoration of cropland at a large scale.