This paper analyzes the function of preventing soil erosion of the different woodlands according to a long-term fixed-position observation, and points out that the steep slope plantation of uncontrolled measures for soil and water conservation is apt to produce sediment Forestland has very strong effect in soil and water conservation when the biomass of arbor in the hillslope is over 1 4.51t/ha. Through analyzing the function of soil and water conservation about forestland (arbor, bush and the mixed wood of arbor and bush), it can be known that if the high forest coverage reaches 40%, forests will provide better protective function. To vegetation under forest, litter layer, herb and sparse forest land which do not suffer destruction from human beings, they all have good function in preventing erosion, and the amount of soil loss is far less than the tolerance of soil erosion. At the same time, when vegetation coverage and biomass are in an appropriate state, they will have powerful protective function. This paper analyzes the function of preventing soil erosion of the different woodlands according to a long-term fixed-position observation, and points out that the steep slope plantation of uncontrolled measures for soil and water conservation is apt to produce sediment Forestland has very strong effect in soil and water conservation when the biomass of arbor in the hillslope is over 1 4.51 t / ha. Through analyzing the function of soil and water about about forestland (arbor, bush and the mixed wood of arbor and bush), it can be known that if the high forest coverage reaches 40%, forests will provide better protective function. To vegetation under forest, litter layer, herb and sparse forest land which do not suffer destruction from human beings, they all have good function in preventing erosion, and the amount of soil loss is far less than the tolerance of soil erosion. At the same time, when vegetation coverage and biomass are in an appropriate state, they will have powerful pro tective function.