| Three Gorges Reservior Area , located in the upper reaches of Yangtze River, is a fragile as well as an important compound ecological transition zone, which is a typical case in terms of its complexity of natural environment, fragility of ecosystem in China. The building of Three Gorges dam has directly or indirectly resultes in its regional degraded vegetations, and problem of the soil and water loss is becoming obviously, which is posing a serious threat to the ecological security and regiongal sustainable development in upper reaches of Yangtze River. The fundamental theoretical research on soil and water conservation functions of different vegetations is to provide evidence for vegetation construction in Three Gorges Reservoir Area and even in Yangtse River Basin.Associated with the national eleventh-five year plan of state key task of scientific and technological research"Technology Research and Demonstration of Vegetation Construction with landscape ecology of shelterbelt system in Three Gorges Reservoir Area, Yangtse River Basin", this paper selects five Artificial Forestlands in Simian mountain as subject, and carries on the reseach on the soil and water conservation of canopy , litters and soil layers by investigating in this region and combining multivatiate statistics such as modeling, statistical method, the ideal-point method, sensitivity. Based on the establishment of multilayer index system, this paper also evaluates the functions on soil and water conservation and analysis the sensitivity. The main conclusions this paper comes to are as follows:(1) Cunninghamia lanceolata pure forest and mixed broadleaf-conifer forest of Cunninghamia lanceolata, Pinus massoniana and Schima superba had the best soil and water Conservation Function of the canopy. In the same rainfall condition, Cunninghamia lanceolata pure forest had the maximum interception rate, mixed broadleaf-conifer forest of Cunninghamia lanceolata, Pinus massoniana and Schima superba took second place. The canopy interception rate takes on down trend with the increase of rainfall amount, and the maxium rate occurred in the about 40mm of precipitation. Maximum moisture capacity of both that of branches and leaves of 5-type of forest in Siman Mountain was also Cunninghamia lanceolata pure forest and mixed broadleaf-conifer forest of Cunninghamia lanceolata, Pinus massoniana and Schima superba.(2) The best soil and water conservation function of the litter layer of 5-type of forest in Siman Mountain was broadleaf forest of Lithocrpus glabra and Schima superba, and Cunninghamia lanceolata pure forest was the worst. Maximum Water-holding capacity of broadleaf forest of Lithocrpus glabra and Schima superba litter was 25.43mm, which was approximately 8 times of retention ability of Cunninghamia lanceolata pure forest(3.17mm). The roughness coefficients of conifer forest of Cunninghamia lanceolata and Pinus massoniana litter was 0.237, which was highest of 5-type of forest in Siman Mountain. Broadleaf forest of Lithocrpus glabra and Schima superba took the second place, and the roughness coefficients of conifer forest of Cunninghamia lanceolata pure forest was the lowest, which was only 0.032.(3) The water-retaining capacity and the anti-scour coefficient of soil, the soil initial infiltration rate and stable infiltration rate were the most important indexes of soil horizon, which could impact soil and water conservation function of 5-type of forest in Siman Mountain. Except soil stable infiltration rate, All the four indexes of Cunninghamia lanceolata pure forest was the best, and broadleaf forest of Liguidambar Formosan, Schima superba and Cinnamomum camphora took the second place. Soil stable infiltration rate of broadleaf forest of Liguidambar Formosan, Schima superba and Cinnamomum camphora was best(5.25 mm/min).(4) Evaluating indicator System of forestry soil and water conservation function in Simian Mountain had been established based on canopy, litters, soil and landform layers. Based on a normalizing approach to 19 attribute values and the additive weighting model, Ideal Point Method was used to give evaluation of soil and water conservation function of 5-type of forest in Siman Mountain. It indicated that Cunninghamia lanceolata pure forest had the best effect on soil and water conservation function, that Because of Cunninghamia lanceolata pure forest grown longer than other forests. Except Cunninghamia lanceolata pure forest, quantity gradation of the other forests was reached: broadleaf forest of Lithocrpus glabra and Schima superba>broadleaf forest of Liguidambar Formosan, Schima superba and Cinnamomum camphora>mixed broadleaf-conifer forest of Cunninghamia lanceolata, Pinus massoniana and Schima superba>conifer forest of Cunninghamia lanceolata and Pinus massoniana.(5) According to sensitivity analysis,5-type of forest in Siman Mountain were divided into two groups. Cunninghamia lanceolata pure forest and conifer forest of Cunninghamia lanceolata and Pinus massoniana were in the same group. They had few sensitivity indexes and functions of soil and water conservation were stable. If we wanted to improve the effect of soil and water conservation, we need to regulate forest structure and . The other group concluded broadleaf forest of Lithocrpus glabra and Schima superba, broadleaf forest of Liguidambar Formosan, Schima superba and Cinnamomum camphora and mixed broadleaf- conifer forest of Cunninghamia lanceolata, Pinus massoniana and Schima superba. They have more sensitivity indexes and their values were higher. soil initial infiltration rate, conglobation degree of soil were the most sensitivity indexes. The evaluation of their soil and water conservation functions were not stable. Reasonably forest improving and rebuilding could enhance their effects evaluation.
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