Abstract:The humic composition(HA and FA),light density of humic acid,combined forms of the soils in the stands of broadleaved forest and Chinese fir stand of the first,the second,the third planting were studied comparatively.The results indicated that,with the substitution of Chinese fir plantation for broadleaved forest and the increasing continuous planting of Chinese fir,the soil organic matter and humus decreased,the ratio of HA to FA and E4 value went down,E4/E6 increased,loosely and tightly combined humus contents and its ratio descended.The soil humus quality declined obviously,which is one of the main reasons for soil degradation at the sites with continuous planting of Chinese fir.