N, P and combined N-P were added to a declining population of Spartina anglica Hubbard in coastal China. Some growth parameters and eco-physiological responses of S. anglica to different treatments were documented. The fertilizer addition had a highly significant effect on the dynamics of its height-growth, the number of leaves, the number of roots and total biomass; however, only N addition had significant effect on leaf area and the leaf thickness in all fertilizer addition. For the dynamics of its height-growth, the effect of N was most apparent; the effect of N-P was not greater than those of N and P separately. The fertilizer addition treatments all enhanced the photosynthesis rate. For the three series of fertilization treatments, the highest N, highest N-P, and medium P yielded the highest photosynthetic rates. The rates were higher by 19.08 μmol•m^-2•s^-1, 15.47 μmol• m^-2•s^-1 and 11.23 μmol• m^-2•s^-1 than that of CK respectively. After freshwater stress for 14 days, treatments made the activity of SOD and POD increase. Effects of medium N and P was significant for SOD activity, However, POD activity of high N and N-P were distinctly higher. In a word, fertilizer addition improved the growth of declining populations of S. anglica, which indicated the decline of S. anglica was correlated with the nutriment deficiency in soil, especially lack of N.