Soil carbon (C) plays a critical role in the global C cycle and has a profound effect on climate change. To obtain an in-depth and comprehensive understanding of global soil C changes and better manage soil C, all meta-analysis results published during 2001-2019 relative to soil C were collected and synthesized. The effects of 33 influencing factors on soil C were analyzed, compared and classified into 5 grades according to their effects on soil C. The effects of different categories of influencing factors, including land use change (LUC), management and climate change, on soil C and the underlying mechanism were compared and discussed. We propose that natural ecosystems have the capacity to buffer soil C changes and that increasing C inputs is one of the best measures to sequester C. Furthermore, a comparison between the meta-analyses and previous studies related to soil C based on bibliometric analysis suggested that studies on wetland soil C, soil C budgets and the effects of pollution and pesticides on soil C should be strengthened in future research.