<p>Extreme rainfall frequently triggers landslides in vegetated areas, and exploring the mechanical properties of rooted soil is critical for understanding such hazards. Using Chinese fir, the most prevalent plant species in Northern Guangdong, as the research subject, this study investigates the mechanical behavior of rooted soil via triaxial tests, with a specific focus on how root characteristics, including root biomass, root angle, and root diameter, regulate the shear strength, deformation, and instability of the soil. Results indicate that roots enhance soil shear strength and inhibit contractive deformation, with this effect becoming more pronounced as root biomass increases, as the angle between roots and potential failure planes grows larger, and as root diameters decrease. Furthermore, roots suffering tensile stress alter the movement patterns of soil particles, increasing the likelihood of soil dilation. However, under conditions of low root biomass and coarse roots, roots are prone to fracture or slippage, causing the soil to revert to a contraction state. The experiments also indicate that roots effectively mitigate soil static liquefaction induced by rainfall infiltration, thereby reducing the likelihood of landslide fluidization. This study contributes to the establishment of constitutive models for rooted soil and provides theoretical support for the treatment of this type of landslide.</p>