The dynamic characteristics of soil carbon and nitrogen contents were investigated under four N treatments (N0, no N input treatment; N1, low N input treatment; N2, middle N input treatment; and N3, high N input treatment) in a Suaeda salsa marsh in the high tidal flat of the northern Yellow River estuary from April to November in 2014. Generally, the contents of SOC, TN, NH4+—N and NO3-—N under different N input treatments generally increased with increasing depth. Compared with other N input treatments, the highest contents of SOC and NO3-—N of each soil layer occurred under the N2 treatment and the highest contents of TN and NH4+—N of each soil layer occurred under the N3 treatment. Although the dynamics model of TN and NH4+—N contents in soil were not altered by different N input treatments, they were increased with the increase of nitrogen loading. Different N input treatments could alter the dynamic change model of SOC and NO3-—N contents in soil. The appropriate input (N1 and N2) significantly increased the contents of NO3-—N in soil, while the excess N input (N3) was not benefit for the accumulation of NO3-—N. Furthermore, the surface soil (0—20 cm) from different N input (especially N2 and N3 treatments) showed a significantly higher SOC contents than those from N0 treatment (P＜0.05) after mid-July, indicating that the continuous input of exogenous nitrogen may not be favorable to the chemical conversion of SOC in soil. This study suggest that wetland environment is conducive to soil nitrogen mineralization when the nutrient situation in S. salsa marsh reaches N1 and N2 level in the future, which in turn can improve the supply of soil nitrogen nutrients. This study also highlights the continuous input of nitrogen loading may inhibit the chemical conversion of SOC, which in turn can help to improve the carbon sink function of S. Salsa marsh.