In order to study the grouting diffusion law and reinforcement mechanism of split grouting with fill medium, a set of three-dimensional simulation grouting test system composed of test bench, grouting system and information monitoring system was designed to carry out the test study of split grouting with fill medium. By observing the properties and distribution characteristics of the grouting veins after grouting, the diffusion law and reinforcement mechanism of the slurry in the filling medium were analyzed. Uniaxial compression test, light dynamic penetration test, permeability test and laboratory soil test were carried out on the soil before and after grouting, and the relationship between the partition characteristics of different properties of slurry veins and the mechanical properties of fill was discussed, and the reinforcement effect of fill grouting was evaluated. Finally, the rationality and reliability of the model test and reinforcement effect evaluation were verified by an engineering example. The results show that there are three types of grouting veins: trunk grouting, branch grouting, and permeable grouting. The injected soil body is strengthened by the three-stage grouting vein network of the mentioned vein types and the compaction between soils. After the grouting, the uniaxial compressive strength of the filling soil increased by an average of 186%, and the permeability coefficient decreased by an average of 47 times. The cohesion and internal friction angle increases by 45.3% and 44.9%, respectively. The bearing characteristics reflectes by a dynamic contact test are consistent with the distribution of grouting veins.