Abstract: In order to study the water inrushing mechanism of floor reinforcement working face and the grouting effect in water abundant mining area of North China Coalfield, by means of mechanical formula derivation, hydro-geological characteristics analysis, micro-seismic monitoring and transient electromagnetic detection results, the superimposed water control mechanism of structure stability key layer of floor and the key layer of failure and penetration in the floor reinforced by grouting is studied, and the model of “two key layers” is formed. The engineering criterion of 2 types and 7 factors that affecting the water control capacity of the “two key layers” is proposed, and the engineering research is carried out in Jiaozuo Mining Area. The results show that the strength of rock mass increases by 40%-159% after grouting, and the maximum tensile strength and shear strength of rock mass reach 5.78 MPa and 38.31 MPa respectively, the floor deformation is reduced, thus reducing the damage and penetration degree of the floor, reaching the engineering criterion of the key layer for the stability and water control of the floor structure. The failure of the key layer of water control through penetration plays a filling and inhibiting role in fracture development, which can prevent confined water inrush. Meanwhile, the insufficient effective waterproof thickness and fault reactivation are the main reasons for the water control failure of the “double key layer”.