In order to study the flow and diffusion law of inorganic fire extinguishing materials in the coal body in the goaf of underground coal mine, to carry out the viscosity study of inorganic materials mixed with water and the analysis of fire extinguishing performance in the early stage, a grouting test platform was built in the laboratory, sand and stone were used to simulate broken coal body, and orthogonal tests were designed to carry out multiple groups of grouting tests. The influence of grouting pressure, water-cement ratio and pore ratio on grout diffusion radius is analyzed, and the variation of grout diffusion radius with the change of water-cement ratio is discussed under the action of grouting pressure. The results show that the 3d grouting test platform can satisfy the grouting test of loose sandstone under different grouting pressures. It is found that the influence of grouting pressure, water-cement ratio and pore ratio on grout diffusion is not linear relation, but multiple power function relation. The corresponding grout diffusion radius formula is constructed, and the factors affecting the grout diffusion range are analyzed. The grouting pressure and water-cement ratio have significant influence on grout diffusion. The results can provide a reliable basis for grouting design of inorganic fire extinguishing materials in goaf.