We studied Pinus elliottii, Casuarina equisetifolia, Eucalyptus urophylla × E. grandis, Acacia cunninghamia and A.aulacocarpa plantations in the coastal sandy land of Fuzhou City, and determined stable carbon and nitrogen isotope abundance values (δ¹³C, δ¹⁵N) in unevenaged leaves (new and oldyear leaves) and topsoils (0-10 cm). we studied the relationship between stable carbon and nitrogen isotope abundance, water use efficiency and soil nitrogen saturation in order to reveal the mechanism of water use efficiency, nitrogen saturation and the difference of carbon and nitrogen cycle rate of different species. The results showed that: (1) the δ¹³C values in leaves of different tree species ranged from -31.682‰ to -29.323‰ in the sequence as P.elliottii>A.cunninghamia>C.equisetifolia>A.aulacocarpa> E.urophylla × E. grandis. The δ¹³C values in newyear leaves were higher compared with those in oldyear leaves for most species, except for E.urophylla × E. grandis. The variation range of δ¹⁵N in leaves of each tree species was from -5.548‰ to -2.167‰ with the highest value in A.cunninghamia, followed by, A.aulacocarpa, C.equisetifolia, P.elliottii, and E.urophylla × E. grandis. The δ¹⁵N values in newyear leaves were higher compared with those in oldyear leaves. (2) The variation range of δ¹⁵N in the topsoils of different tree species was from -4.675‰ to -2.975‰ with the highest value in A.aulacocarpa, followed by, A.cunninghamia, C.equisetifolia, E.urophylla × E. grandis, and P.elliottii. However, there was no significant difference in the C content in the topsoils of different tree species. (3) The water use efficiency of P.elliottii, C.equisetifolia, A.cunninghamia and A.aulacocarpa decreased with the aging of leaves. The water use efficiency of newyear leaves of different tree species varied from 39.09 μmol·mol^-1 to 76.57 μmol·mol^-1, with P.elliottii> A.cunninghamia> C.equisetifolia>A.aulacocarpa>E.urophylla × E. grandis. The water use efficiency of oldyear leaves varied from 38.56 μmol·mol^-1 to 62.59 μmol·mol^-1, with P.elliottii>C.equisetifolia>A.cunninghamia> E.urophylla × E. grandis>A.aulacocarpa. (4) The water use efficiency of different tree species was significantly positively correlated with that of new leaves, indicating that the water use efficiency of newyear leaves plays a more significant role. The water use efficiency of stand was also affected by stand type.