Abstract：The farming-pastoral zone in Naiman Banner is located in the hinterland of of Horqin Sandy Land. The research on the formation mechanism and background value of groundwater hydrochemistry supports the allocation of water resources and the green development of agriculture and animal husbandry. Based on hydrogeological survey and hydrogeochemical analysis, combined with self-organizing map neural network (SOM) and K-means clustering hybrid algorithm, this study revealed the characteristics of groundwater chemical composition, main controlling factors and environmental background values. Results indicated significant spatial heterogeneity in groundwater chemistry, with HCO3-Ca·Mg as the predominant hydrochemical type and weakly alkaline characteristics. Groundwater chemical evolution is primarily driven by dissolution-precipitation of carbonate minerals and weathering of silicate minerals, and controlled by alternating positive cation adsorption. The apparent background values of Total Fe (TFe), F- , TDS and NO3-N, key indicators affecting the quality of groundwater in Naiman Banner, were 0.42~0.56 mg/L, 0.34~0.38 mg/L, 181~188 mg/L and 0.22~1.58 mg/L, respectively, which were estimated by using a coupled approach of hydrogeochemical graphic method, Grubbs test and SOM. The high background of TFe may be related to siderite dissolution, while the F- enrichment is controlled by fluorite dissolution and alternating positive cation adsorption. This research elucidates the groundwater background values and hydrochemical formation mechanisms in the farming-pastoral zone of Naiman Banner, providing scientific support for the optimization management of regional water resource, pollution prevention, and ecological conservation.