Abstract：Substrate-root system complex (SRSC) is the main functional part of the eco-engineering for rock slope protection. It is important content for eco-engineering mechanism exploration to evaluate the interactional characteristics of SRSC quantification ally by mechanics. This paper discusses the interactional mechanics characteristics of SRSC from experiment. The shear and tensile strength of SRSC and the shear strength between complex and rock are both studied；the relationship of shear and tensile strength and factors of root amount and water content are also researched；the effects of time scale is discussed in the end. The results show that the shear resistance between SRSC and rock consists of friction and biotic force. The shear strength decreases with water content increasing while reduces with root amount increasing. They represent logarithm functional relationship. Water content influences on both friction and biotic force，but the latter is the main influenced aspect. The complex has tensile strength due to root system. The tensile strength increases with root amount enhancing while decreases with water content increasing. They represent relatively notable functional relationship. The reinforced effect and friction enhance with root amount increasing，whereas reduce with water content increasing. The relationship between shear strength(τ) and vertical pressure(s) accords to Coulomb law. Besides general physical significance of shear strength indexes，j and c include the effect of root system. In the case of the same water content and vertical pressure，shear strength and root amount represent exponential functional relationship. The values of j and c increase with the total amount of root system enhancing. So the shear strength of complex will be elevated markedly. In the case of the same root amount and vertical pressure，shear strength and water content represent power functional relationship. The values of j and c decrease with water content enhancing. So the shear strength of complex will decline. The interactional mechanical characteristics of the rock-substrate-root system exhibit a significant time scale effect with plant developing，and it gets stable after 5 months of seeding when Cynodon dactylon is concerned. It is an essential support to renew the theory of the eco-engineering for rock slope protection and to apply it.
