In order to study the contents and dynamic characteristics of soil light and heavy fraction organic carbon during the vegetation degradation process, the filed and laboratory experiments were conducted in marsh meadow of Gahai wetland in Gannan state, Gansu province. The main results were as follows:The soil light fraction organic carbon contents in 0-20 cm layers varied in different stages of vegetation degradation of marsh meadow, following the order of UD (undegraded) > LD (lightly degraded) > HD (heavily degraded) > MD (moderately degraded). The soil light fraction organic carbon in 20-100 cm layer was less effected by vegetation degradation. The soil heavy fraction organic carbon contents HD and MD stages of vegetation degradation were significant higher than UD and LD in entire soil layer (P<0.05). With the increasing soil layers, all the soil light and heavy fraction organic carbon contents significantly decreased. The soil light and heavy fraction organic carbon showed the obvious dynamic characteristics with time in all stages of vegetation degradation. The soil light fraction organic carbon contents gave a trend of "down-up-down" in UD stages of vegetation degradation in 0-20 cm soil layer, i.e., the highest in May, the lowest in July and September. But the contents were reduced and stabilized in June in the other stages of vegetation degradation. The variations of soil light fraction organic carbon contents was small in 20-100 cm soil layers. The variations of soil heavy fraction organic carbon contents were consistent in all stages, giving linear decreases with time, the significant difference occurred between different months (P<0.05). These findings indicated that vegetation degradation could result in the decreases of soil light fraction organic carbon, and the increases of heavy fraction organic carbon. However, the main consumption of soil organic carbon is the light fraction, and the heavy fraction is relatively stable. Correlation analysis showed that the changes of underground biomass and soil moisture contents had significant influence on soil light and heavy fraction organic carbon.