Vetiveria zizanioides (hereafter vetiver) is one of the few species that survived in the water-level fluctuation zone of the Three Gorges Reservoir. Although the introduction, cultivation, and research of vetiver in China has a history of decades, little is known about the adaptive strategies of vetiver that under the conditions of long-term flooding and drying periodic changes. Therefore, the plasticity in phenotype and biomass allocation of vetiver planted in altitude zones of 166-169 m, 169-172 m and 172-175 m above sea level in the water-level fluctuation zone of the Wushan section of the Three Gorges Reservoir in 2008 were studied in 2016. The results showed that:(1) the morphological traits (e.g.,number of tillers, average plant height, number of internodes, length of internodes, number of leaves per tiller, number of leaves per bush and length of leaves) of vetiver in altitude zone of 166-169 m were all lower than those in altitude zones of 172-175 m and 169-172 m. The number of internodes in altitude zone of 166-169 m was significantly different (P<0.05) from those in other two altitude zones (169-172 m and 172-175 m). (2) Compared with other two altitude zones, the number of roots in altitude zone of 166-169 m was the least while the length of roots was the longest. (3) The number of tillers without internodes in altitude zone of 166-169 m was the most, and the difference was significant with those of other two altitude zones (P<0.05). (4) The total biomass of vetiver in altitude zone of 172-175 m was the largest, followed by 169-172 m and 166-169 m altitude zones, and the difference between 166-169 m and 172-175 m altitude zones was significant. The ratio of underground to aboveground biomass and stem to leaf biomass were the lowest in altitude zone of 166-169 m. (5) The biomass of leaves, living stems and withered stems in the upper part and the root biomass in different soil layers were the highest in altitude zone of 172-175 m, followed by altitude zones of 169-172 m and 166-169 m. There was no significant difference in soil physical and chemical properties in different altitude zones. The difference in morphological traits and biomass of vetiver in different altitude zones was mainly attributed to the impacts of periodic alternate flooding and drying. Reducing plant height, controlling plant component size, and reducing biomass were beneficial to reduce the energy consumption of vetiver grow in low altitude area during flooding. While reducing the number of roots and prolonging the length of roots were beneficial to enhance the adsorptive capacity of nutrients and water during drying. Additionally, the biomass of vetiver in the low altitude zone was allocated more to the aboveground parts, especially leaves, which was conducive to photosynthetic production and carbohydrate accumulation and could lay the material foundation and energy reserve for future rapid recovery and growth of vetiver. These adaptive strategies were important for long-term survival and growth of vetiver in the water-level fluctuation zone of the Three Gorges Reservoir.