Salicornia europaea L., a euhalophyte, needs moderate concentrations of NaCl (200-400 mmol/L) to maintain its optimal growth. The assimilation of nitrogen under salinity might be distinctive in this plant. In present study, S. europaea plants were hydroponically cultured in medium containing moderate Na⁺. Nitrate, ammonium and urea with nitrogen concentrations ranged from 0.1 to 400 mmol/L were separately applied to S. europaea plants in culture medium, to investigate the characteristics of nitrogen assimilation. Measurements on growth and photosynthetic parameters, nitrogen metabolic enzymes activities, as well as the content of soluble and unsoluble protein, nitrate, ammonium and total nitrogen, were performed after treatments for 30 days. The results showed there was no significant difference in growth of S. europaea plants when supplied with the three nitrogen forms at nitrogen concentrations of 0.1 and 1 mmol/L. However, when the concentration of nitrogen reached to 10 mmol/L or higher, nitrate proved to be the best nitrogen nutrition for the growth of S. europaea, followed by ammonium and urea. When nitrogen concentration increased to 50 mmol/L, the growth of S. europaea supplied with ammonium and urea were significantly inhibited, while the plants maintained normal growth until high nitrate nitrogen concentration of 400 mmol/L under salinity of 400 mmol/L Na⁺. Under all three forms of nitrogen, photosynthetic parameters were consistent with the plant growth trends. Root volume and activities were normally distributed and raised to the peak at the nitrogen concentration of 10 mmol/L with nitrate, 1 mmol/L with ammonium and 1 mmol/L with urea, respectively. The nitrogen metabolic enzymes activities in S. europaea were affected by exogenous nitrogen concentration. The nitrate reductase and glutamine synthetase activities were increased with nitrate supply. However, ammonium and urea did not affect nitrate reductase activities. The glutamine synthetase activities were normally distributed under ammonium and urea, which was highest at the concentration of 10 mmol/L nitrogen in ammonium and 50 mmol/L in urea, respectively. The content of total nitrogen, soluble and unsoluble protein of S. europaea was increased with the increasing supply of exogenous nitrogen. In summary, this study revealed that S. europaea has a strong ability on nitrogen absorption and utilization. All the three forms of nitrogen with a wide range of nitrogen concentration can be used as nitrogen supply for S. europaea, among them, however, nitrate with nitrogen concentrations from 0.1 to 400 mmol/L was proved to be the best, followed by ammonium and urea whose acceptable nitrogen concentration ranged from 0.1 to 50 mmol/L. These findings act as basis for revealing the mechanism of nitrogen absorption and assimilation in S. europaea, which will in turn be meaningful for developing the halophytes in coastal and other saline areas.