The diversity of geological structure combinations in the coal seam floor makes it difficult to characterize, prevent and control floor water inrush in the Chenghe mining area in the Weibei coalfield, China. Based on a comparative study of the structure of the floor strata and the sedimentary characteristics of the no. 5 coal seam floor in the Chenghe mining area, the floor strata were categorized into four types. Fluid–solid coupling numerical simulation software was used to study floor water-blocking performance. We found that mining failure depth was the shallowest and water-blocking capacity was the best for the “soft-hard-soft” type of floor, followed by two interbeds of soft and hard type floors, while the mining failure depth was the deepest and the water-blocking capacity the worst for the “hard-soft-hard” type of floor. These conclusions were applied to guide the floor grouting reconstruction project at the 22,507 working face in the Dongjiahe coal mine. The “hard-soft-hard” type of floor was transformed into an "interbedded soft and hard" type of floor with a better water-blocking capacity, avoiding blind grouting, reducing grouting costs and the risk of water inrush, and allowing safe mining above the confined aquifer. The research results revealed how floor strata combinations control the water-blocking characteristics of the floor and provides scientific guidance for floor reinforcement and grouting projects.