Abstract: Aiming at understanding the effects of salinity and nitrogen addition on growth and biomass allocation of Phragmites australias seedling in Momoge National Nature Reserve, we conducted a pot experiment with four levels of N addition(0, 11.25, 45 and 90 g·m^-2 NH₄NO₃) and salinity(0, 5‰, 10‰ and 15‰ NaCl) treatments.Our results showed that:(1) salinity had significant effects on the seedling growth, but not on biomass.With salinity increasing, the individual height, leaf area and special leaf area of the seedling decreased, and the shoot-root ratio increased, while aboveground, belowground and total biomass increased first and then decreased.(2) N addition had significant effects on individual height, leaf area, aboveground, belowground and total biomass, but not on special leaf area and root-shoot ratio.With the increase of N concentration, the individual height, leaf area, aboveground, belowground and total biomass of the seedlings increased significantly while special leaf area and root-shoot ratio decreased.(3) the interaction of salinity and N addition had no significant effects on seedling growth and biomass allocation, but increasing N concentration could promote seedling growth and biomass accumulation under all salinity treatments(0-15‰).Our study demonstrated that increasing N concentration moderately in the growth stage would be a feasible regulatory approach for Phragmites australias in salt marsh to alleviate the damage caused by salt stress.