Abstract: To reveal the diffusion form and law of backfill grouting in loess shield tunnel, considering the characteristics of shield tail, a model test system with real-time monitoring for water content, seepage pressure and soil pressure and visualization of diffusion process is established. Considering the different moisture content of loess, the grout diffusion form and the variation law of moisture content, seepage pressure and soil pressure in grouting process are studied through model tests. The results show that under the same dry density, different moisture content has a significant effect on the diffusion form of backfill grouting. When the moisture content is 10 %, the grout does not diffuse obviously, and the grout-soil forms an obvious interface. Only the moisture content at the interface changes significantly, and the soil pressure of each layer is large. When the water content is 20 % and 30 %, the grout diffusion range increases, the moisture content of each layer of soil changes, the soil pressure and seepage pressure appear step curves, and obvious grout veins are formed in the soil. The grout diffusion forms in loess shield tunnel are mainly compaction diffusion, pressure filtration diffusion and splitting diffusion.