Roots affect the soil stress and strain and contribute to soil reinforcement. An analysis of stress and strain in the root-soil composite is presented which combines roots, soils, and an interface element by using the Duncan-Chang E- model and a nonlinear-interface-element model. In this research, a finite element numerical analysis method was applied to simulate the stress field resulting in a composite of Pinus tabulaeformis roots and soils. Results show that roots can transmit the stress from surface soils to deep soils, and can reduce soil stress within the surface soil layer; results also show that the effect of soil reinforcement by roots is limited to surface soils. The Slope Safety Index of a pine slope becomes 10% higher than that of a natural slope, indicating that roots have a significant effect on soil reinforcement. Roots affect the soil stress and strain and contribute to soil reinforcement. An analysis of stress and strain in the root-soil composite is presented which combines roots, soils, and an interface element by using the Duncan-Chang E-model and a nonlinear- In this research, a finite element numerical analysis method was applied to simulate the stress field resulting in a composite of Pinus tabulaeformis roots and soils. Results show that roots can transmit the stress from surface soils to deep soils, and can reduce soil stress within the surface soil layer; results also show that the effect of soil reinforcement by roots is limited to surface soils. The Slope Safety Index of a pine slope becomes 10% higher than that of a natural slope, indicating that roots have a significant effect on soil reinforcement.