Abstract：Four kinds of plants including Myrsine，Vitex negundo，Bauhinia，Pogonatherum paniceum，grew on according to different weathering degrees of bedrock，and were selected to measure pull-resistances，mechanical characteristics of single root and biological indexes by the in-situ pull-out experiment. The purpose is to study the mechanical characteristics of interaction between the root system of plants and rock for rock slope protection. The results indicate that the pull-resistance of shrub is impacted by configuration of the root system，maximum pull-resistance of single root and the amount of roots under stress. The maximum pull-resistance increases with root diameter increasing，and there is a good power function relationship between them. The relationship between pull force and tensile stretch of single root changes with different vegetation types. Furthermore，the maximum tensile stretch varies with different root diameters. The pull force-tensile stretch of Bauhinia jaberi oliver and Vitex negundo is of linear relationship，which fallows Hook¢s law，while that of Myrsine africana is of logarithm function relationship. The maximum tensile stretch of Bauhinia jaberi oliver and Vitex negundo is declined with increment of root diameter. The relationship between the maximum tensile stretch and root diameter appears a unimodal curve. If the diameter at ground height(DGH) or plant height is similar，the pull-resistance of plants increases with bedrock weathering degree. If the rock weathering degree is similar，the pull-resistance and some factors such as DGH，plant height and subterranean biomass show positive correlations and present exponential function relationships. However，there is no obvious mathematic relationship between biological factors and the pull-resistance of Pononatherum paniceum，and the mechanical effect between Pononatherum paniceum and bedrock is not distinct. As a result，the research result can provide reference to the structural design of eco-engineering for rock slope protection(EERSP) and selection of vegetation type.
