Abstract: To address the frequent occurrence of rockbursts during the excavation of main roadways in deep geological structural zones, this study integrates theoretical analysis, numerical simulation, and engineering practice to investigate the mechanism of floor rockbursts in a main roadway located at the synclinal axis of a kilometer-deep mine. The main conclusions are as follows: the syncline structure promotes the increase in maximum principal stress, and this effect becomes more pronounced with increasing burial depth. The tangential and axial stresses of the surrounding rock directly beneath the roadway floor at the synclinal axis reach peak values, driving progressive failure of the coal-rock mass from shallow to deep and forming two dominant fracture planes. Fracture plane I consists of tensile and tensile-shear failures in shallow coal, whereas fracture plane II is formed by shear and compressive failures in deeper coal-rock mass. The latter serves as the primary pathway for stress transfer and fracture propagation in the floor and is the key fracture plane governing rockburst instability. The thick floor coal and its underlying strata at the synclinal axis can be divided, from top to bottom, into the rockburst manifestation zone, energy accumulation zone, and initiation zone. Under syncline-induced horizontal compressive stress, the rock mass in the initiation zone undergoes fracturing and dilation, which triggers deformation and failure of the overlying energy accumulation zone, leading to rapid elastic energy accumulation and stress concentration. Once the strength limit is exceeded, stress and energy are instantaneously released, causing dynamic ejection of coal in the manifestation zone and ultimately resulting in rockburst occurrence. After implementing an optimized prevention and control scheme covering the initiation, energy accumulation, and manifestation zones of the floor, the maximum and average floor deformation were reduced by more than 50%, and the number of high-energy events decreased from 12 to 3 per 200 m of roadway excavation. This effectively alleviates stress concentration and reduces the rate of elastic energy release, thereby ensuring safe excavation of the main roadway at the deep synclinal axis. The results provide a reference and theoretical basis for rockburst prevention under similar geological and mining conditions.