【Objective】To study the effects of nitrogen (N) form on growth and physiological parameters of Hibiscus hamabo under different levels of salt stress, the salt tolerance and underlying mechanism of H. hamabo under two N forms were discussed. This provides basis for improving application technology of H. hamabo greening in salt-alkaline land. 【Method】A glasshouse experiment was conducted to study the growth characteristics, photosynthesis, N and K⁺ content of H. hamabo under the combined effects of N forms ( {\mathrm{NH}}_4^{+}-N, {\mathrm{NO}}_3^{-}-N), and salt stress. Coastal soils were collected at four salt stress levels: control, low, medium and high.【Result】After 90 days of the stress treatment, all the plants died under the high salt treatments. In the medium salt treatments, plant height, ground diameter, stem biomass, leaf and the whole plant were significantly reduced. However, no significant effects on growth were observed following the low salt treatments. Both {\mathrm{NH}}_4^{+}-N and {\mathrm{NO}}_3^{-}-N increased the growth, net photosynthetic rates and N content of H. hamabo, among which {\mathrm{NH}}_4^{+}-N increased the biomass in the control treatments, but decreased K⁺ content. Under the low and medium salt stress, {\mathrm{NO}}_3^{-}-N application significantly increased the biomass of roots and whole plant and K⁺ content.【Conclusion】Under salt stress, two N forms were both beneficial to H. hamabo biomass, and could improve its salt tolerance to a certain extent. The difference was that {\mathrm{NO}}_3^{-}-N could effectively promote the growth of roots, while {\mathrm{NH}}_4^{+}-N had a significant effect on the growth of above-ground plant parts. Compared with {\mathrm{NH}}_4^{+}-N at the same level of salt stress, {\mathrm{NO}}_3^{-}-N was more beneficial to alleviate the inhibition of salt stress on H. hamabo. Therefore, the application of {\mathrm{NO}}_3^{-}-N under salt stress is able to maintain the balance of nutrient and ion content, improving the photosynthetic function, and eventually enhancing the salinity tolerance of H. hamabo.