Abstract: To characterize cropland soil acidification and its associated factors in a representative major grain-producing area of the Huang-Huai-Hai Plain, we conducted a case study in Xiping County, Henan Province, China. Based on paired, point-to-point resampling of 101 sites in 2008 and 2025, we quantified changes in soil pH, nutrient status, cation exchange capacity (CEC), and particle-size composition. Extreme gradient boosting (XGBoost) models were used to identify soil properties closely associated with soil pH and its temporal change, while data on exchangeable acidity and exchangeable base cations collected in 2025 were further analyzed to elucidate the relationships between soil acid–base status and exchangeable ion composition across sampling sites. From 2008 to 2025, the mean cropland soil pH decreased from 7.13 to 5.94, representing a decline of 1.19 units, and more than 90% of the sampling sites exhibited varying degrees of acidification. Over the same period, soil organic matter, total nitrogen, available phosphorus, and available potassium increased by 25.0%, 38.9%, 353.2%, and 70.5%, respectively, indicating that soil acidification occurred concurrently with nutrient accumulation. The XGBoost model showed significant out-of-sample predictive ability for changes in soil pH. Clay content, total nitrogen, available phosphorus, CEC, soil organic matter, and total phosphorus exhibited relatively high predictive importance; however, these statistical associations do not necessarily imply direct acidifying effects. In 2025, the mean exchangeable acidity was 1.04 cmol/kg, of which exchangeable aluminum accounted for 66.1%. Across the spatial gradient observed in 2025, exchangeable acidity, exchangeable aluminum, and acid saturation were significantly negatively correlated with soil pH, whereas exchangeable calcium, total exchangeable bases, and base saturation were significantly positively correlated with soil pH. These findings demonstrate that cropland soil acidification is widespread in Xiping County and has occurred alongside substantial nutrient accumulation. Nitrogen cycling may contribute to net acid inputs, whereas soil texture, organic matter, and CEC are closely associated with soil acid-buffering capacity. Because exchangeable ion data for 2008 and long-term agricultural input records were unavailable, long-term changes in base cations and the relative contributions of different acidification sources require further investigation. These results provide a scientific basis for monitoring cropland soil acidification and implementing spatially targeted prevention and mitigation strategies across the Huang-Huai-Hai Plain.