To explore the response of plants at different altitudes to water and the changes of plant adaptability under climate change, we chose the typical tree species, Litsea cubeba, Corylopsis sinensis, Camellia japonica and Symplocos stellaris, in the natural succession at different altitudes in the Lushan Mountain as the research objects. We used hydrogen and oxygen isotope technology, combined with the Iso-source model, to quantify the proportion of water source contribution. The results showed that: (1) The δD value of soil water and plant water showed different seasonal characteristics, and the δD value in the dry season was more depleted than in the rainy season. The altitude effect of soil water and plant water δD value was not obvious, and the δD value of soil water generally presented the surface enrichment and deep depletion. (2) As the altitude increased, the main water sources of plants were different. In the rainy season, the ratio of Litsea cubeba to the surface layer (0—10 cm) soil water gradually increased, and the ratio of Camellia japonica to the lower layer (30—50 cm) soil water gradually increased. During the dry season, the absorption ratio of Corylopsis sinensis to surface soil water gradually decreased. (3) There were seasonal differences in the main water sources of plants, and the performance of the same plants at different altitudes was also different. At the area of 1 287 m above sea level, the contribution rate of surface soil moisture (0—10 cm) to Corylopsis sinensis in rainy season was 68.50%, while only 9.00% in dry season. However, Camellia japonica’s contribution rate changed from 3.10% to 76.50%. At the area of 1 078 m above sea level, with the alternating rain and drought, Litsea cubeba changed from uniform (0—50 cm) absorption of soil water to preferential use of surface layer (82.20%) for soil water, Corylopsis sinensis changed from mainly absorbing and utilizing the upper layer (0—20 cm, 74.40%) soil layer to uniform water, Camellia japonica from the deep layer to the upper layer (66.18%), and Symplocos stellaris from the lower layer to the surface layer (86.40%). At the area of 884 m above sea level, in the rainy season, the main water sources of Litsea cubeba, Camellia japonica, and Symplocos stellaris were 10—40 cm (88.20%), 40—50 cm (91.80%), 0—50 cm; but the surface layer was used first in the dry season. (4) Soil surface water had a certain contribution to Camellia japonica, but its contribution was lower than those of Litsea cubeba, Corylopsis sinensis, and Symplocos stellaris. 40—50 cm soil water was the main water source of Camellia japonica, and it kept coordinated growth with the other three plants; however, the other three tree species had certain water competition, and the competition degree was different at different altitudes. In summary, plant water sources had the altitude differences and seasonal effects to adapt to the constraints of different environmental factors. Camellia japonica had a coordinated water use strategy with Litsea cubeba, Corylopsis sinensis, and Symplocos stellaris. Litsea cubeba, Corylopsis sinensis, and Symplocos stellaris had water competition and the degree of competition varied at different altitudes. This research provides a scientific theoretical reference for the allocation and protection of tree species in the subtropical ecosystem, and the establishment of a coupling model of vegetation eco-hydrology in Lushan Mountain.