To preliminarily investigate the adaptation mechanism of Taxodium Rich. plant ‘Zhongshanshan 406’ under complete submergence stress and analyze the effect of leaf gas film in this process, two treatments ［maintaining the gas film (GF+) and removing the gas film (GF-)］ were set up, 8 d of complete submergence stress was applied, and leaf hydrophobicity, underwater net photosynthetic rate, phyllosphere bacterial community characteristics, etc. were analyzed. The results show that, with the extension of submergence time, leaf hydrophobicity of ‘Zhongshanshan 406’ decreases obviously. On submergence for 0 d, the water droplet contact angles on the adaxial and abaxial sides of leaves in the GF+ group are 128.02° and 124.15°, respectively, and the gas film thickness is 25.64 μm; on submergence for 8 d, the three indexes decrease to 85.40°, 96.43°, and 0.52 μm, respectively, and the gas film disappears. With the extension of submergence time, the number of adherents on the leaf surface continuously increases, the palisade and spongy tissue cell structures of leaves undergo obvious deformation or rupture, and the intercellular space increases. On submergence for 1-8 d, the stomatal apertures in the GF+ group (0.87-0.97 μm) are significantly (P<0.05) higher than those in the GF- group (0.60-0.69 μm). Leaf gas film significantly enhances the underwater net photosynthetic rate in the early stage of submergence. On submergence for 0 d, the underwater net photosynthetic rate of the GF+ group is 3.3 times that of the GF- group, with an extremely significant difference (P<0.01); on submergence for 1 d, the underwater net photosynthetic rates of the GF+ and GF- groups are 1.00 and 0.84 μmol·m^-2·s^-1, respectively, showing a significant difference; on submergence for 8 d, the difference in underwater net photosynthetic rate between the GF+ and GF- groups is not significant, but both are significantly higher than those on submergence for 1 and 3 d. On submergence for 1-8 d, the dominant phylum of epiphytic bacteria gradually shifts from Pseudomonadota to Cyanobacteria, while Pseudomonadota remains the dominant phylum of endophytic bacteria. Under the same submergence time, the bacterial community compositions of the GF+ and GF- groups are highly similar, indicating that the leaf gas film does not significantly affect the overall bacterial community structure. The results of twoway analysis of variance and principal coordinate analysis (PCoA) both indicate that submergence time is the dominant factor driving the diversity variations and structural reorganization of the phyllosphere epiphytic bacterial community. The study reveals that ‘Zhongshanshan 406’ can effectively maintain a high underwater net photosynthetic rate through leaf gas film in the early stage of complete submergence, and the synergistic effect of the short-term protection of leaf gas film and the bacterial community constitutes an important mechanism for rapid adaptation of ‘Zhongshanshan 406’ to complete submergence stress.