Abstract: For the problem of grouting and plugging water in Chengjiao Coal Mine, the indoor grouting experiment is used to simulate the grouting project on site. The grouting effect of three kinds of ultra-fine cement grout with different viscosity is compared. The grouting test was carried out on the single fracture specimen of argillite sandstone to test the bonding strength recovery ability and impermeability after the grouting of the single fracture specimen of sandstone, and to evaluate the grouting effect at a macro level. By means of SEM scanning and digital image processing technology, the characteristic porosity of the sandstone single crack specimen before and after grouting is counted, and the grouting effect is evaluated microscopically. The research shows that the bond strength of the optimized low-viscosity slurry increased by 35%, the water seepage rate decreased to 1.39 mL/h, and the cross-sectional characteristic porosity reached the minimum value of 1.31%, indicating that the optimized group of low-viscosity ultra-fine cement slurry has good grouting effect.