Sedimentary-metamorphic iron deposits in North China commonly exhibit synformal ore-controlling structural characteristics. However, the ore-controlling mechanism and genetic link between fold deformation processes and iron enrichment remains unclear. This work is based on an integrated analysis of the spatiotemporal distribution, metallogenic tectonic setting, ore-controlling structural patterns, layer-thickness variation coefficients, mineral morphological fabrics, and ore grades of sedimentary-metamorphic iron deposits. A coupled relationship between the metallogenic tectonic environment and synformal structures was revealed. The primary synformal basal morphology of tectonic basins promoted the early development of synformal structures in sedimentary strata, and the later folding deformation and metamorphism result in the dominant feature of synformal ore-controlling structures. Taking the Shuichang iron deposit in eastern Hebei and the Jianshan iron deposit in Shanxi as examples, the research shows that fold deformation caused differential deformation of quartz and magnetite in the original Banded Iron Formation (BIF). Magnetite layers, being more susceptible to plastic flow, migrated and accumulated in low-pressure zones at fold hinges, leading to a relative increase in magnetite-layer thickness and an improvement in ore grade. The evolution of synformal ore-controlling structures can be divided into three stages: primary sedimentation, fold deformation, and tectonic uplift. Subsequent uplift and erosion resulted in the weathering and destruction of antiformal portions, while synformal structures were preserved, thereby establishing them as the most universal prospecting indicators in the region.