The processes of carbon cycling in wetlands have been affected by increasing nitrogen (N) input derived from anthropogenic activities, and concern is growing over the effects of nitrogen input on carbon stability. So far, the overwhelming studies concentrated on the relationships between the amount of N addition and the stability of soil organic carbon (SOC). However, much less information is known how various N forms affect the stability of SOC in wetlands. We reviewed the effects of N forms on the fixation of CO_2, soil autotrophic and heterotrophic respiration, soil methane emission, and the temperature sensitivity of SOC decomposition. Firstly, the results indicated that the selective utilization of N forms for plant species may change the photosynthetic rate, fixation of CO_2, and thus autotrophic respiration rate. Moreover, the return of plant litter and its quality, such as C/N ratio, may be varied under the input of different N forms, these can affect litter decomposition and soil heterotrophic respiration rate. Secondly, the input of various N forms may produce different effects on soil pH and the activities of soil microorganisms and enzymes, which may change soil heterotrophic respiration rate. Thirdly, the decomposition of SOC fractions may have varied responses to various forms of N input, but we have known little about this. Fourthly, the effect of various nitrogen forms on plant biomass, soil ph and redox may affect the input of available C and N from plant to soil and thus microbial activity, changing methane emission. Fifthly, atmospheric N deposition and global warming simultaneous affect soil carbon cycling. However, there is still no answer about the combined effect of N forms and temperature on SOC decomposition, although this issue is very important. So far, many uncertainties still exist in the relationship between N input and SOC stability, and there is litter studies distinguishing the effect of N forms SOC stability in wetlands. Therefore, much more attention should concentrate on distinguishing the effects and mechanisms of N forms on SOC stability, so as to further know the relationship between N deposition and SOC stability.