Based on experimental data of dynamic response characteristics of foundation bed packing for Shuohuang Railway, a PFC2D saturated coarse-grained soil dynamic triaxial numerical model was established, and linear cement particle contact was selected to reflect the cohesive characteristics of the coarse-grained soil and the mud blowing was studied from the perspective of micromechanics and geometry. Mesoscopic mechanism of disease formation. The results show that the numerical model can better reflect the dynamic response characteristics of coarse-grained soil. Vibration load changes the contact load between the soil particles and the particles, destroys the bonding bonds between the particles, forms free particles and pores, causes the softening of the foundation bed, and finally forms the mud and mud disease. The smaller the confining pressure and the bonding between the soil particles, the easier the sample will soften and the formation of mud-flushing disease. The strengthening of the foundation bed should be taken from two aspects: improving the confining pressure state of the surface of the foundation bed and the track bed and increasing the bonding strength between particles.