Abstract: Aimed at addressing the issues of slurry leakage and difficulty in forming an effective slurry cake during slurry shield tunneling in highly permeable sandy strata, this study systematically carried out slurry infiltration and cake formation tests. It deeply investigated the required slurry performance indicators for forming a high-quality slurry cake when using seawater-based slurry versus freshwater-based slurry in high-permeability sandy formations, analyzed the influence patterns of slurry properties on the cake formation process, and proposed a targeted optimization of the slurry formulation, ultimately recommending the optimal slurry mix ratio suitable for such strata. The research results show that: The bentonite content in seawater-based slurry has a significant impact on slurry density: the higher the bentonite content, the greater the slurry density and the lower the filtration loss.CMC content is the key factor in controlling slurry viscosity. Although increasing bentonite content can also increase viscosity, its viscosifying effect is far less than that of CMC. To meet the construction requirements of highly permeable sandy strata in cross-sea tunnels, the final optimized slurry mix ratio is determined as∶bentonite mass∶CMC mass∶soda ash mass: seawater mass = 100∶3∶6∶700.