The Lianyunshan-Hengyang fault is a typical representative of regional NE-trending deep major faults, extending for 430 km within Hunan Province. Along this fault, numerous mineral deposits and large-scale fault basins have developed, rendering it highly significant in terms of resources and economic value. However, research on its overall vertical and lateral structural composition, the temporal context of its formation, and its dynamic mechanisms remains limited. In light of this, this paper conducts a comprehensive study of the fault"s structural composition, tectonic attributes, formation age, and dynamic mechanisms through field structural investigations and analysis of existing regional geological and geophysical data. The results indicate that the Lianyunshan-Hengyang fault is a composite structural zone composed of numerous faults of varying orders, scales, attitudes, ages, and properties and fault basins from deep to shallow levels. Geophysical exploration data, including regional gravity, aeromagnetic, seismic, and geothermal data, reveal the presence of a continuously extending large fault zone at depth along the Lianyunshan-Hengyang fault. At the surface, the Lianyunshan-Hengyang fault manifests as a large-scale fault zone, 10–25 km wide, consisting of a NE-trending main fault, Cretaceous-Paleogene fault basins on the northwestern side (hanging wall) of the main fault, and secondary basin-controlling faults with various strikes within and along the basin margins. The NE-trending main fault is composed of five NE-trending faults that are offset end-to-end from northeast to southwest, along with connecting faults oriented NEE and SN. The faults within the zone can be classified into six types based on strike: NE, NNE, SN, NW, EW, and NEE. These faults primarily formed as thrust and strike-slip faults under early Indosinian NW-compression, late Indosinian SN-compression, and early Yanshanian NWW-compression, and controlled the development of fault basins during the Cretaceous extensional activity. Under the NW–SE extensional environment of the Cretaceous, the various NE-trending main faults and connecting faults underwent inherited extensional activity, forming a continuous NE-trending large surface fault and an extended fault basin, thereby giving rise to the Lianyunshan-Hengyang deep major fault. The primary dynamic mechanism for regional extension is the circular mantle flow induced by the retreat of the ancient Pacific subducting slab. Mantle upwelling and horizontal flow of asthenospheric material associated with this mantle flow led to lithospheric extension and thinning.