[Objective] Yunnan Province is rich in forest resources, thus posing an important part of China's forest carbon pool. Its forest ecosystem plays an irreplaceable role in the global carbon cycle and balance, and its organic carbon pool in the forest soil does too in regulating the global carbon balance and slowing down the rising concentration of atmospheric chamber gas. Though soil humus is known to be the main body of soil carbon, it is still unclear as to characteristics of its composition and influencing factors. Therefore, it is of great significance to strengthen the study of composition of the forest soil humus and its influencing factors to the efforts of regulating forest soil carbon balance and improving soil fertility.[Method] A total of 88 soil samples were collected from the topsoil layers of different forest zones in Yunnan province. Environmental factors of the sampling sites, such as soil type, latitude and longitude, elevation, slope degree and slope aspect, were measured through field investigations. The soil samples were analyzed in lab for contents of soil carbon and soil humus and its components, of which regression analysis and descriptive statistics were employed to quantify relative contributions of elevation, soil type, slope degree, slope aspect, annual mean precipitation and annual mean temperature to the variation of soil humus composition. In the end, soil humus composition and distribution in the forest soils of Yunnan were characterized.[Result] Results show:in the top soils of the forests, SOC content varied in the range from 8.40 to 199.73 g·kg^-1, with a mean of 51.37 g·kg^-1; HE-C content in the range from 2.54 to 84.02 g·kg^-1, with a mean of 24.52 g·kg^-1; HA-C content in the range from 0.99 to 33.64 g·kg^-1, with a mean of 9.35 g·kg^-1; FA-C content in the range from 1.40 to 57.16 g·kg^-1, with a mean of 15.17 g·kg^-1; and H/F in the range from 0.17 to 4.59, with a mean of 0.78; soil humus in the samples was fairly low in polymerization degree, with C/N ranging from 4.68 to 41.72 and averaged to be 14.25. The contributions of soil type, elevation and annual mean temperature to soil humus composition were significant(P<0.01 or 0.05), but those of annual precipitation, slope degree and slope aspect were not so significant(P<0.05). The environmental factors varied in explanation of the spatial variation of total organic carbon, extractable humic carbon, humic acid carbon, fulvic acid carbon, and carbon-nitrogen ratio in the soil with soil type explaining 30.1%, 29.6%, 30.9%, 24.3% and 11.5%; annual mean temperature doing 22.2%, 19.5%, 13.7%, 18.8% and 18.0%; elevation doing 13.3%, 9.4%, 11.1%, 8.7% and 13.9%, respectively.[Conclusion] The content of soil organic carbon in the forest soils of Yunnan is found to be relatively high in the northeast and northwest parts of the province, and relatively low in the south and central parts. Soil type, elevation and average mean temperature are the key factors regulating spatial variability of the soil humus in the forests of Yunnan Province. In terms of contribution degree, the factors exhibit an order of soil type > annual mean temperature > elevation. Soil type plays an important role in the accumulation of humus in the forest surface soil.