| The soil organic carbon (SOC) under 11 forest types such as pinus massoniana forest, rubour mixed forest and shrubs of the Three Gorges reservoir area (TGRA) were studied. Method of soil type was chosed to calculate the SOC pool of the main soil types as the background pool of the SOC under 11 forest types, and method of vegetation type was chosed to calculate the SOC pool under 11 forest types. Fraction and distribution of SOC under main forest types, and the control factors of SOC in this paper were studied too. Major conclusions were summarized as follows:(1) The SOC density of the TGRA of 0～20 cm was 3.20 kg/m~2, the total SOC storage was 190.48×10~6 t; SOC density of 0～100 cm was 12.59 kg/m~2, the total SOC storage was 750.51×106 t. The SOC densities of yellow soil, yellow-brown soil and dark brown soil were higher than those of other soil types, and the SOC densities of purple soil and skeleton soil were the lowest.(2) Based on the data of forest inventory, the forest types of the TGRA were divided into 11 types of vegetation by its dominant tree species and acreages, such as Pinus massoniana forest, mixed forest of Quercus, and Shrubs, etc. The concentrations and densities of SOC under 11 types of vegetation were significantly different and generally decreased with depth. The average soil thickness of 11 types of vegetation was 56.3～98.5 cm, the soil thickness of forest of Cunnighamia Lanceolata was the largest (98.5 cm), and that of shrubs was the smallest (56.3 cm). The total storage of SOC under 11 main types of forest types in the TGRA was 366.36 ×10~6 t, with 22.90 %, 18.36 %, 28.33 % and 30.41 % in 0～10, 10～20, 20～40 and >40 cm soil depth interval, respectively. The densities of SOC under every vegetation type in the west of the TGRA were higher than those in the east of the TGRA. It changed counter to the trend of cover rate of forest vegetation in the TGRA.(3) The total carbon storage of litters under main forest types of the TGRA was 1150.31×10~4 t. The biomass of litter under cunnighamia lanceolata forest was the most of 11 forest types, and that of forest of Citrus reticulate, Citrus aurantium and Citrus grandis was the least. Content of litters under 11 forest types was 379.70～514.91g/kg. The study results show that the biomass was related with SOC, but the relationship was not significant.(4) The study on methods of determing of WSOC indicated that the method of ring sampler infiltration was practicable. The total storage of WSOC of the main forest types of the TGRA detrmined by ring sampler infiltration method in this paper was 6.528×10~6 t. The storages of WSOC under 11 forest types were as follows: Pinus massoniana forest 2.43 ×10~6 t , robur mixed forest 1.57 ×10~6 t, shrubs 1.22×10~6 t, Cupressus funebris forest 0.46×10~6 t, Cunninghamia lanceolata forest 0.60×10~6 t, Citrus reticulate plantation 0.38×10~6 t, other soft broad leaved forest 0.22×10~6 t, the broad leaved and coniferous mixed forest 0.22×10~6 t, Neosinocalamus affinis 0.16×10~6 t, other hard broad leaved forest 0.20 ×10~6 t, temperate Pine forest 0.06×10~6 t.(5) Contents of ASOC, SSOC and RSOC under 11 forest types occupied SOC with 2.2 %～6.0%, 46.6 %～81.3 % and 16.1 %～50.0 % , respectively. ASOC, SSOC, RSOC and WSOC under every main forest type in the TGRA were close related to SOC. The contents of SSOC and RSOC in upper soil layer werer higher than those in underlayer, but content of ASOC did not change with depth.(6) The contents of SOC were negative associated with soil temperature in 5 cm, 15 cm and 20 cm soil layer at 4 stations: YiChang, WanZhou, FuLing and ChongQing. The relationship of SOC and soil temperature were not significant, because of the small span in geography of the TGRA and the little difference among the averages of 30 years of soil temperature at 4 stations.(7) The contents of SOC were negative associated with soil texture and soil bulk density significantly. The regression equation of SOC and soil texture: Y = 27.69 - 3.88 X(R~2 = 0.146); the relationship between SOC and soil bulk density could be described by equation: Y = 56.221 - 29.506X(R~2 = 0.361) . The results of this paper also indicated that soil pH and content of soil water and soil nutrients had a very important influence on SOC. Soil pH and the soil coefficient of drying were negative associated with SOC, while soil nutrients and soil quality content of water were positively associated with SOC significantly.(8) Gradient and elevation had a positive influence on SOC under serval main forest types of the TGRA, while the factor of aspect had a negative influence on SOC. Analyse of linear regression indicated that the description veracity of regression equations changed with forest types and soil layers.(9) In five years after the beginning of the project of Grain for Green, the concentration and inventory of SOC in the 0～30 cm soil layer under most reafforestation patterns were higher than those under cropland conditions, while the concentration and inventory of SOC in the 0～60 cm soil layer did not change or even decreased in some cases. The concentration and inventory of SOC and the decreasing magnitude of SOC with the soil profile depth under all the studied reafforestation patterns were lower than those under shrubbery land conditions, which received the least impact of land use change. It is thus suggested that the impact of the five-years reafforestation patterns on the SOC in the 0～60 cm soil layer is insignificant.
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