Abstract: The failure characteristics of the coal seam floor under mining are significantly influenced by the lithologic combination and structural arrangement of the underlying strata. For the typical double-layer floor structure, composed of upper and lower rock layers with significantly different mechanical properties, commonly found in the North China-type coalfields, traditional single-layer floor structure to accurately characterize the failure characteristics. Therefore, it is crucial to reveal the failure mechanism of complex bedrock layer structures. In this study, mining factors such as burial depth and mining height are incorporated into a plastic slip failure framework to explain how mining conditions control the depth and geometry of plastic slip failure in structurally complex floors. Representative cases are further used to quantify the extent to which the stratigraphic structure constrains the floor failure depth. A numerical model is developed to account for the stress environment adjustment induced by goaf caving and compaction. The results show that floor failure is dominated by shear, and that the stress adjustment during goaf compaction does not alter the failure mode. The failure characteristics of the coal seam floor under mining for different bedrock types have been clarified. The influence of lithology and thickness on floor failure has been systematically understood, revealing that the primary factor determining floor failure is the position and thickness of soft rock layers. By comparison with field measurements of floor failure depth, the relative errors of the theoretical analysis and numerical simulations are -6.8% and 6.9%, respectively, supporting the scientific validity and reliability of the proposed approach. These findings provide a theoretical basis for floor stability control and risk mitigation in scenarios such as close-distance coal seams and the safe extraction of seams overlying confined aquifers.