Effective diffusion of slurry during pulsating grouting is crucial for improving the overall efficiency of seepage control projects. Based on the basic theory of two-phase Darcy’s law, a numerical model is established to simulate the pulsating grouting diffusion process under seepage conditions. The effects of parameters such as final pressure, duration, as well as successive period and intervals of pulsating grouting on the grouting of porous media are analyzed under seepage conditions. The results show that the slurry driven by the pulsating grouting pressure scatters both in the diffusion region against the flow and the diffusion region with the flow. When grouting for 300 seconds, the diffusion radius of the region with the flow is 2-4 times that of the region against the flow. As the final pressure of pulsating grouting increases and the duration advances, the diffusion distance of the slurry increases logarithmically, and the diffusion range and slurry concentration increases gradually. When grouting for 900 seconds, the diffusion radius of the slurry in the region with the flow at the final pressure of 2.4 MPa is 23.5 times that at the final pressure of 0.4 MPa. When grouting for 300 seconds, the diffusion radius and diffusion opening of the slurry in the region against the flow reach stability. When the final pressure of pulsating grouting is 2.4 MPa, the diffusion radius and diffusion opening of the slurry in the region against the flow are 5.9 and 5.6 times higher than when the final pressure is 0.4 MPa, respectively. As the successive period of pulsating grouting increases from two to ten seconds, the diffusion distance of the slurry increases logarithmically. As the pulsation interval increases from two seconds to eight seconds, the diffusion distance of the slurry decreases logarithmically.