This study investigated the spatial characteristics of chemical weathering in the Horqin Sandy Land by analyzing 118 surface sediment samples. Multiple chemical weathering indices (e.g., CIA, WIP, PIA), compositional variability index (ICV), and geochemical ternary diagrams were employed to evaluate weathering intensity and explore controlling factors. The results indicate that: (1) The Horqin Sandy Land is in the initial stage of chemical weathering, with no significant differences in weathering degree among sediment types. Slightly higher weathering intensity in the southwestern and central regions corresponds to low-maturity sediments dominated by first-cycle deposits. Plagioclase weathering prevails, characterized by sodium and calcium depletion stages. (2) Provenance discrimination using ternary diagrams and binary discriminant functions reveals that sediment geochemistry aligns with intermediate-acid granite sources, indicating parent rocks primarily derived from intermediate-acid magmatic terrains. Provenance lithology dictates initial weathering conditions, thereby regulating subsequent weathering processes. (3) Climate has a significant influence on the differences in spatial weathering: chemical weathering intensity in the western region correlates with temperature, whereas precipitation governs the eastern region. Sedimentary differentiation further modifies CIA values, amplifying the spatial heterogeneity in weathering intensity. This study enhances the understanding of surface material migration mechanisms and ecological evolution in arid-semiarid regions.