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 paper, an anti-seawater deterioration slurry using flaxseed gum as an admixture was proposed. Based on the self-developed variable cross-section infiltration column, the effects of flaxseed gum content and seawater intrusion degree on cumulative water filtration and excess pore water pressure were studied, respectively. The cumulative particle size distribution and rheological properties of slurry at different seawater concentrations were obtained. The mechanism of infiltration and filter cake formation of anti-seawater deterioration slurry was analyzed. Results showed that flaxseed gum could improve the effect of fluid loss reduction, accelerate the dissipation of excess pore pressure, and promote the formation of mud film. With the increase of seawater intrusion, the fluid loss decreased first and then increased, the d85 of slurry increased first and then decreased, and the rheological property gradually deteriorated. When the intrusion degree was less than 30%, the slurry can resist the seawater deterioration and the particle clogging was the key to the formation of dense filter cake. After the intrusion degree reached 50%, the filter cake permeability became worse. The coupling effect of particle clogging and rheological blocking may be the reason for inhibiting the continuous penetration of the slurry into the formation. When the intrusion degree was 100%, the slurry properties 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.