Abstract: In the deep mining process of North China type coalfield,the threat of floor water damage is more and more serious. The use of horizontal hole grouting technology is the principal means to control this kind of water damage,and the study of the slurry diffusion law is of great significance in the design and construction of grouting engineering. The existing research mainly aims at the problem of slurry diffusion in horizontal fractures with vertical hole grouting. When horizontal hole grouting is employed in engineering,the diffusion law of slurry is different from that of a vertical hole. Therefore,the diffusion law of grouting slurry in horizontal holes of fractured rock mass was studied,and the pore and fracture system in a fractured rock mass was equivalent to the fracture with the same opening,and the equivalent fractured rock mass model was constructed. The mechanical model of grout diffusion in the horizontal hole was established by selecting the equivalent single crack,and the pressure time-space distribution equation of the equivalent single crack with any dip angle in the grout diffusion area was derived when considering the grout self weight. Then the theoretical relationship between grouting pressure and grouting time and diffusion distance was obtained. COMSOL was used to establish a three-dimensional numerical calculation model for the vertical fracture of the horizontal hole grouting,and the calculation and analysis were carried out for two working conditions considering gravity and without gravity. When gravity was not considered,slurry diffusion morphology was axisymmetric circular diffusion,and when gravity was considered,the slurry was preferentially diffused along the direction of gravity. Under the influence of gravity,the effect of groundwater on the dispersion and transportation of slurry was stronger in the process of slurry diffusion. Gravity has a great influence on the diffusion pattern,diffusion distance and final grouting pressure of a horizontal hole grouting. By comparing the theoretical analysis and numerical results of both the grouting pressure and grouting time,the variation trends of grouting pressure and grouting time,grouting final pressure and diffusion distance obtained by the two are basically consistent,and the error between the theoretical and numerical calculation results is controlled at about 10%,which further verifies the established level hole grouting the correctness of the grout diffusion model. The research results can provide scientific basis for the design of grouting final pressure,grouting method and diffusion distance in horizontal hole grouting engineering. 