Increasing soil organic carbon (SOC) levels play a critical role in agricultural sustainability and, maybe more important, in mitigating greenhouse effects and global climate changes. The mechanisms of SOC stabilization are associated with the capacity of SOC sequestration, and studies in this field will help the governments make efficient policies and decisions to reduce greenhouse gas emission. This paper gives a brief review of four stabilization mechanisms of SOC: (1) recalcitrance of organic carbon compounds, (2) interactions with metal oxides and soil mineral surfaces, (3) spatial inaccessibility against decomposers because of micro-aggregate′s physical protection, and (4) biological mechanisms, mainly the direct contributions of soil organisms themselves. Until now there are contradictorily results regarding the dominant SOC stabilization mechanisms, possibly depending on factors, such as ecosystem and soil type, soil depth, soil managements, as well as soil biological activity and community composition. The authors will consider future research proposals with an emphasis on a comprehensive understanding of all four mechanisms of SOC stabilization, and will pay more attention on roles of soil bio-community.