This study aimed to reveal the fluid resistance mechanism of Phyllostachys rivalis (Phyllostachys rivalis), a bamboo species, and provide a theoretical basis for its application in vegetation restoration of wetlands and areas with fluctuating water tables. We investigated the biomass and contents of the main nutrient elements in annual Phyllostachys rivalis rhizome-roots by using individually potted Phyllostachys rivalis with artificial irrigation for water supply and waterlogging in the third, sixth, and twelfth months. The nutrient contents, stoichiometric ratio, and nutrient accumulation were analyzed, and the following results were obtained: the contents of N, P, and K in Phyllostachys rivalis rhizome-roots decreased significantly under waterlogging in the third month. However, no obvious impact was noted on the contents of C, Ca, Fe, and Mg and C/P, N/P, and N/K. The nutrient contents, stoichiometric ratio, and nutrient accumulation altered markedly with prolonged waterlogging. Meanwhile, the contents of C, N, P, and Ca and C/K, N/K, and P/K decreased, and the contents of K, Fe, and Mg and C/N, C/P, and N/P increased with prolonged waterlogging. The accumulation of nutrients was significantly inhibited before waterlogging in the sixth month. However, the accumulation of nutrients showed a significant increase under waterlogging in the twelfth month; this was mainly because of significant increase in the root biomass. Thus, we showed that maintaining strong nutrition stability is a strategy of Phyllostachys rivalis in response to environmental stress. The rhizome-roots of Phyllostachys rivalis can sustain high nutrient absorption and accumulation through producing large numbers of roots, both in soil and water, and show adaptive regulation of the nutrient stoichiometric ratio in response to environmental stress. Since Phyllostachys rivalis can survive in long-term waterlogged environments, it could be used for vegetation restoration of wetlands and areas with fluctuating water tables. In addition, it may play an important role as one of the bamboo species that can be used for purifying eutrophic water bodies.