Water inrush risk prediction and evaluation of seam roof and floor are the foundation of water inrush disasters prevention in coal mines. According to the waterproof medium conditions of seam floor, the mechanical properties of coal-measure rock and the lithology, structure and thickness of seam floor were analyzed; the theory and methods of water inrush risk evaluation of seam floor were founded. It is shown that the waterproof medium conditions of seam floor depend on the lithology of aquifuge and the structure. Statistical analysis showed a second power functional relationship between the limit water pressure (p) of seam floor and the thickness of aquifuge of seam floor (h).The lithology and structure characteristics of the aquifuge were considered.