Abstract: To clarify the mechanism of floor-type rockburst in the haulage roadway during inclined slicing mining of a large-dip-angle ultra-thick coal seam, the 37221-1 working face at Dongxia Coal Mine is selected as the engineering background. Field monitoring, numerical simulation, and theoretical analysis are integrated to investigate the mechanism of rockburst induced by static–dynamic load superposition. First, PFC numerical simulations are conducted to investigate the evolution of force chains and stress distributions under static and dynamic loading, and a spring–slider model of floor failure is established based on the simulation results. Subsequently, the characteristics of mining-induced stress distribution following upper-stage extraction are analyzed, and a stress transfer model of the overlying strata along the dip direction is developed to quantify the static stress concentration in the stage coal pillar. Based on seismic wave propagation characteristics, a peak particle velocity (PPV) attenuation model is established to estimate the vibration velocity of dynamic disturbances reaching the roadway. A dynamic amplification factor is then introduced and determined through comparative FLAC3D simulations to achieve a more refined estimation of dynamic stress increments. Finally, seismic moment tensor inversion is performed to identify the source rupture mechanisms of rockburst events. The results indicate that, during inclined slicing mining, roof stresses are transferred to the floor through the stage coal pillar, resulting in high static stress concentrations around the haulage roadway of the 37221-1 working face. Meanwhile, the hard floor exhibits a greater energy storage capacity than the roof and is more susceptible to failure under the combined effects of high vertical stress and strong tectonic stress following coal extraction. The intense seismic waves generated by floor failure interact with the concentrated static stresses around the stage coal pillar, ultimately triggering floor-type rockburst in the haulage roadway. Furthermore, the asymmetric and staggered confinement imposed by roof and floor stresses, together with the increased difference between vertical and horizontal stresses following protective seam mining, makes the floor coal–rock mass more susceptible to shear failure.