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