The southeastern Sichuan-Western Hunan-Hubei fold thrust belt, located in the central-upper Yangtze region of South China, attracts significant scientific interest due to its substantial natural gas resources and intense structural deformation. Previous studies extensively examined the belt's tectonic origin, mechanisms, and structural styles, yet controversies persist regarding the impact of pre-existing structures on its tectonic evolution. Employing high-resolution seismic reflection interpretation profiles and discrete element numerical modeling, four comparative models were constructed incorporating the pre-existing Huayingshan fault, Qiyueshan basement lithological partitioning, and multiple detachment layers. These models investigated the formation of the Huayingshan and Qiyueshan faults, systematically revealing spatio-temporal control laws of pre-existing structures over regional deformation evolution. Simulation results indicate closest alignment with present-day structural configurations when integrating the Qiyueshan basement partitioning. During initial tectonic activity, rapid uplift east of the Qiyueshan basement differentiation boundary formed an incipient domal structure, contrasting with minimal deformation near the Qiyueshan basement differentiation boundary. Under prolonged tectonic stress, the domain east of this boundary experienced compressional thickening dominated by thick plastic basement, developing a synclinorium fold belt. Conversely, western domains governed by rigid basement and multilayered detachment systems formed an anticlinorium fold belt. At the terminal deformation phase, the synclinorium belt underwent gradual uplift with westward migration, while anticlinorium deformation terminated near the Huayingshan fault, establishing the extant tectonic framework. Integrated analysis with prior research suggests the Xuefeng Shan orogenic belt supplies the primary driving force for regional deformation. Modulated by Qiyueshan basement partitioning, deformation proceeded through stagewise evolution mediated collectively by multiple detachment layers. The Huayingshan fault is reinterpreted as non-pre-existing, whereas the Qiyueshan fault originates from basement partitioning mechanisms. Specifically, the western Hunan-Hubei fold thrust belt is primarily controlled by the basal detachment layer, while the southeastern Sichuan fold thrust belt is mainly governed by the Cambrian detachment layer. Secondary detachment layers such as the Silurian and Triassic play an adjusting role in both regions, influencing shallow structural patterns.