Abstract: The heavy metal pollution and excess input of nutrient elements become two important environmental problems in mangrove forest. The ecological risk of cadmium(Cd) is relatively high, and ammonium nitrogen(NH₄⁺-N) is the main speciation of nitrogen in sediment of mangrove. In order to clarify the growth and physiological characteristics of Kandelia obovata under combined stresses of Cd and NH₄⁺-N, pot experiments were conducted. Plant growth, leaf photosynthetic parameters(photosynthetic rate(P_n), stomatal conductance(G_s), intercellular CO₂ concentration(C_i) and transpiration rate(E)), leaf malondialdehyde(MDA), leaf soluble sugar, and root activity were determined. The results showed that:(1)Plant growth and leaf transpiration rate(E) of K.obovata decreased under single Cd stress, with root activity to be reduced under higher single Cd stress; (2)Under Cd stress, low concentration of NH₄⁺-N significantly improved growth of root, but did not significantly improved growth of aboveground part, and leaf photosynthesis(P_n, G_s and E); while high concentration of NH₄⁺-N significantly reduced plant growth, and leaf photosynthesis(P_n, G_s and E); (3)Under Cd1 treatment, root activity first increased and then decreased with increasing NH₄⁺-N concentration; while reduced root activity were shown under Cd2 and Cd3 treatments with NH₄⁺-N supply; (4)Under Cd stress, low concentration of NH₄⁺-N did not significantly reduce content of malondialdehyde(indicative of oxidative damage) and soluble sugar(indicating osmotic adjustment), while high concentration of NH₄⁺-N significantly reduced the content of MDA and soluble sugar. Therefore, the lower concentration of NH₄⁺-N can alleviate the Cd toxicity to root, with limited emission on aboveground part; while high concentration of NH₄⁺-N and Cd combined stress would have a synergistic effect to aggravate Cd toxicity to K.obovata.