Abstract: During the construction of offshore and seabed slurry shield tunnels, the properties of slurry contacting with seawater are seriously deteriorated, leading to the failure of filter cake formation and the instability of excavation face. In this study, an anti-seawater deterioration slurry using flaxseed gum as an admixture is proposed. Based on the self-developed variable cross-section infiltration column, the effects of the flaxseed gum content and seawater intrusion degree on the cumulative water filtration and excess pore water pressure are studied, respectively. The cumulative particle size distribution and rheological properties of slurry under different seawater concentrations are obtained. The mechanism of infiltration and filter cake formation of anti-seawater deterioration slurry is analyzed. The results show that the flaxseed gum can improve the effects of fluid loss reduction, accelerate the dissipation of the excess pore pressure, and promote the formation of mud film. With the increase of the seawater intrusion, the fluid loss decreases first and then increases, the d₈₅ of slurry increases first and then decreases, and the rheological properties are gradually deteriorated. When the intrusion degree is less than 30%, the slurry can resist the seawater deterioration, and the particle clogging is the key to the formation of dense filter cake. After the intrusion degree reacheds 50%, the filter cake permeability becomes worse. The coupling effects of the particle clogging and rheological blocking may be the reason for inhibiting the continuous penetration of the slurry into the formation. When the intrusion degree is 100%, the slurry properties are deteriorated seriously, and the filter cake cannot be formed. The research can provide feasible ideas for the research and development on seawater-resistant slurry during the construction of slurry shields under seawater environment.