During the construction of underwater tunnels, the boring of the shields has often to be stopped to check and repair the cutting tools under hyperbaric conditions. However, how to adjust the slurries to form a dense filter membrane on the excavation face so as to maintain the stability of the excavation face is still a problem to be solved. In the paper, experimental study is made on the preparation and filter membrane formation of slurries, with the hyperbaric operation of shield in gravel and sand strata during the construction of Nanjing Yangtze River Tunnel as an example. A series of tests are made on the preparation and filter membrane formation of different slurries. A twosep slurry adjustment program, i.e, firstly, slurry with low density and low viscosity is used to infiltrate into the sand strata, then slurry with large density and large viscosity is used to form a filter membrane on the excavation face, is proposed. The program proposed has been applied in the hyperbaric operation during the construction of Nanjing Yangtze River Tunnel, airtight filter membrane has been formed and the stability of the excavation face has been guaranteed. The experience can provide valuable reference for the slurry preparation in other similar projects.