Soil water level and salinity are the major factors affecting plant growth in the coastal wetlands. It is important to understand the adaptation mechanism of wetland plants to the interactive effect of water level and salinity for the protection and restoration of the coastal wetland in the Yellow River Delta. We examined the responses of plant growth and the characteristics of root biomass of Phragmites australis to the interaction of different water levels (CK, -30 cm, 0 cm, 30 cm), salt concentrations (0%, 1.5% NaCl) and growth stages (germination stage, seedling stage). The results showed that water level and salinity significantly interacted to affect root biomass. Compared with the CK, root biomass under the combination of 1.5% NaCl and 30 cm water level was significantly lower, but no significant differences were observed under the combination of 0% NaCl and 30 cm water level. This result indicated that soil salinity could change the tolerance threshold of P. australis enduring water stress. With the exception of plant height, ecological traits of P. australis at 0 cm water level showed high adaptation. However, 30 cm water table depth had inhibitory effects on some ecological traits of P. australis. The total root biomass of soil surface layer was not sensitive to water level and salinity gradients. With the increasing soil depth, water level and salinity significantly affected the accumulation of root biomass. The highest fibrous root biomass was （6.76±2.19） g per plant under the condition of 0 cm water level, 0% NaCl treated at seedling stage. The lowest fibrous root biomass was （1.09±0.68） g per plant under the condition of 30 cm water table depth, 1.5% NaCl treated at germination stage
