Abstract: The Oligocene Yacheng Formation in the Qiongdongnan Basin (QDNB), northern South China Sea (SCS), is characterized by well-developed coal measures with thin coal seams, poor stability, scattered vertical distribution, and extensive planar coverage. This study investigates the controls on coal seam development through integrated analysis of paleoclimate, astronomical cycles, paleotectonics, and paleogeography during the depositional period. To elucidate the controlling factors and developmental patterns of coal measures in the Yacheng Formation, providing insights for coal and coal-derived hydrocarbon source rock exploration. A comprehensive analysis was conducted on paleoclimate, astronomical forcing, paleotectonics, and paleogeography, with a focus on orbital forcing mechanisms governing coal seam formation. Macro-scale paleoclimate and regional tectonic evolution are primary controls on thick coal measure development, while secondary tectonic-sedimentary conditions and short-term astronomical cycle-driven climate fluctuations govern thin coal seam formation. Active tectonics and climate variability induce lateral shifts in coal-forming environments; short astronomical cycles (eccentricity, precession) create periodic "coal-forming windows" that favor thin coal seam accumulation under suitable secondary conditions. Early Yacheng Formation coal formation occurred in marine-continental transitional fan-delta plain marsh environments during short eccentricity maxima and precession minima, modulated by insolation and monsoonal precipitation. Mid-to-late Yacheng Formation coal seams predominantly developed in tidal flat and lagoon marsh settings during precession or obliquity minima, influenced by insolation, monsoonal precipitation, and Antarctic ice sheet-driven sea-level fluctuations. Two coal-forming theoretical models were established: i) “Peat accumulation controlled by short eccentricity-precession coupled climate forcing” and ii) “Peat accumulation governed by obliquity-driven sea-level oscillations”. These models clarify how astronomical cycle-induced climate evolution interacts with tectonic-sedimentary processes. The refined models reveal the coupled controls of orbital forcing, tectonic-sedimentary dynamics, and climate evolution on coal seam spatiotemporal distribution in low-latitude Paleogene basins, offering a framework for predicting coal resource occurrence in similar settings.