The results of this study indicated that the composition and properties of soil humus were closely related to their formation conditions,and had zonal regularities.Data obtained showed that the composition of soil humus in virgin soils varied with different soil zones.For geographical distribution from black soil to red earth,the optical density elementary composition,C/H ratio and aromaticity of humic acids in the soils all had certain zonal regularities.According to the results mentioned above,the soil humus substances appear to tend to be simple from the north to the south.As compared with the virgin and dry farming soils,paddy soil had a higher content of organic matter and HA/FA ratio,but a lower content of active humic acid.It indicates that the hydrothermal conditions under rice planting are favourable for the aecumulation of organic matter,and change the composition of soil humus.However,the anaerobic condition of paddy soil is a factor inhibiting the decomposition and condensation of organic matter in soil,which results in the formation of humic substances with smaller molecule and low-degree of humification.Calculation of the correlation coefficients between E₄,E₄/E₆ ratio and elementary composition,C/H ratio,oxygen-containing functional groups and aromaticity show that E₄ value is not only significantly correlated with C%,O%,phenolic-OH-O%,quinone O%,but also with C/H ratio and aromaticity.It is also indicated from these results that E₄ value might be regarded as an index of aromaticity of humic acids.