Abstract: A substrate-vegetation system is the primary functional component of eco-engineering for rock slope protection (EERSP).Its stable development relies on the state of nutrient cycling.In this study, Cynodon Rich is selected as the trial plant to study the process of nutrient cycling in a substrate-vegetation system of rock slopes with observation tests simulating rock slopes.The results show that nutrient accumulations in the substrate, which is the main accumulation storage of nutrients, occupy 98% of the system.The total nutrient accumulations in the system are in the following order:K>N>P>Ca>Mg and that in the bio-subsystem are in the order of K>N>Ca>Mg>P;two years after the establishment of vegetation on slopes, biomass accumulation from decayed material reaches homeostasis, which is the basis of nutrient cycling of systems;biocycles of nutrient elements in the system are in the following order:K>N>Ca>Mg>P.The nutrient utilization efficiencies of N, Ca and Mg are higher than those of K and P when absorbing nutrients from substrates.The annual returns of each nutrient element are all greater than that of annual retentions, which indicates that slope vegetation has the characteristic of quick cyclic nutrient utilization.Due to favorable and stable characteristics of the substrate and the vegetation cover, the annual input of nutrients in the system is greater than the annual output of nutrients (runoff), which implies a favorable state of nutrient accumulation.The annual input (except K) of nutrients in the substrate (the litter layer is not included) is also greater than the annual output of nutrients.The annual deficit of K is small but persistent.It is, therefore, not necessary, to supply nutrients from external sources to maintain a stable development of vegetation on slopes.It is shown that the nutrient supply is not a major factor, after appropriate artificial deployment, during the later stages of engineering management.