Twig and leaf are the two most important functional organs of the plant. Under a particular density, their allometric relationship is the result not only of individual development but also of the interplay between the plant and the surroundings. Tamarix gansuensis is one of the key species in harsh environments of arid regions, and the allometric relationship of its twig and leaf plays an important role in resource utilization strategies of wetland plants. In this study, the community of T. gansuensis was divided into three density gradients in Qinwangchuan wetland-low density (0.1-0.35 trees/m²), medium density (0.35-0.6 trees/m²), and high density (0.6-0.85 trees/m²). The relationship between twig and leaf growth and the photosynthetic characteristics of the leaves were studied. Results showed that, with increase in density, soil moisture, plant height, canopy closure, twig length, and leaf area increased, while soil bulk density, pH value, electric conductivity, crown width, branch diameter, bifurcation angle, leaf number, and photosynthetically active radiation decreased. Leaf area index, net photosynthetic rate, transpiration rate, and stomatal conductance increased firstly then decreased. There was a significantly positive correlation (regression slope k > 0, P < 0.05) between twig length and leaf area. With increase in density, the regression slope between the twig length and the leaf number was the same (regression slope k=0.9, P < 0.01), but its intercept was subject to a positive shift along the y axis (Y-intercept was from 0.25 to 1.93). The regression slope between the twig length and the leaf area decreased (regression slope 0.65 ≤ k ≤ 0.98, P < 0.05). These results showed that there was an allometric relationship between the twig and the leaf. With increase in density, the twig-leaf constructive mode of shorter twig length, lower leaf area, larger bifurcation angle, and larger leaf number under low density evolved into the expansion mode of longer twig length, larger leaf area, and smaller bifurcation angle and leaf number under high density. The stomatal conductance, net photosynthetic rate, and transpiration rate increased, while water use efficiency decreased. All these findings reflected the phenotypic plastic adaptation and the resource utilization strategy of the T. gansuensis in arid areas.