Ecological protection has become a trend in slope protection, representing the direction of development in slope protection technology. This paper presents a comprehensive study of the mechanical reinforcement effects of roots on soil, with a specific focus on the root systems of Pennisetum alopecuroides. The study reveals that the reinforcing effect of roots on the peak strength of soil is influenced by multiple factors, including axial pressure (σ), water content (ω), and root area ratio (RAR). A multi-factor quadratic fit was conducted using Design-Expert software, which showed that the F-value of the predictive model is 69.56, with a P-value of <0.0001, indicating the model's high significance. The influence of the three factors on the peak intensity is in the following order: σ>RAR>ω. The study also modifies the vertical root soil reinforcement model (WWM model) to quantify the shear strength increment of soil-root composites. The slope of the fitted line in the modified WWM model is about 0.26. The paper further explores the enhancing effect of plant roots on slopes in extreme environments, dividing the soil layers into shallow reinforcement areas, middle level reinforcement areas, clay, silty clay, and CDW soil. The rainfall intensity was 4mm/h, lasting for 6 days, simulating a severe rainstorm. The displacement of the reinforced slope after six days of heavy rainfall was analyzed.