The content of total organic carbon in soil is a major indicator reflecting the content of total organic matter and further on soil fertility. There are numerous factors that affect accumulation of organic carbon in soil. Among them, iron plays an essential role in "capturing" organic carbon and forming "rust sink", thus promoting accumulation of soil organic carbon. A number of scholars have studied stabilizing mechanisms of soil organic carbon. In this paper, attempts were made to summarize the studies that had been done. It is found that the stabilizing mechanisms mainly include physical preservation of aggregates, chemical preservation of minerals, biological preservation of microorganisms and preservation of organic carbon per se. Among the four mechanisms, the first two are the main ones. Iron is closely involved in the mechanisms of physical, chemical and biological preservations. In physical preservation, iron promotes formation of soil aggregates. In chemical preservation, iron adsorbs and precipitates with organic carbon. At the same time, iron affects activity of soil microorganisms in biological preservation. All indicate that iron plays an important role in soil organic carbon accumulation. And the protective effect of organic carbon per se is mainly reflected in the anti-decomposition of a certain portion of organic carbon. In the end, the authors put forward several suggestions. More attention should be paid to the mechanisms of organic carbon sequestration and functional recovery of the carbon sink in the soil systems that are active in oxidation reduction and remarkable in ecological service function, to quantitative researches on and comparison between the different mechanisms in importance, and to simulation experiments, so as to better realize the goal of theory serving practice.