Slope stabilization by vegetation is an environment-friendly, cost-effective, and sustainable biological engineering measure, which fits in with the new concept of ecological civilization construction. We took the underground system of Moso bamboo and Lei bamboo, which were typical scattered bamboo in subtropical zone of China, as study objects to describe the spatial distribution condition of root systems and to explore the factors affecting the biomechanical properties of underground system. The results showed that the proportion of length and volume for three diameter classes presented the trend of gradual decline with the depth of the soil. More than 80% of roots concentrated in the 0-40 cm soil layer. The proportion of length for D≤1 mm diameter class of root system was the highest. The order of proportion was Lei bamboo rhizome root (83.62%), Lei bamboo basal root (80.46%), Moso bamboo rhizome root (75.70%), and Moso bamboo basal root (70.45%). The proportion of volume for D≥2 mm diameter class of Moso bamboo was the biggest with the rhizome root and basal root being 78.73% and 70.23%, respectively. The proportion of volume for D≥2mm and D=1-2 mm diameter classes for Lei bamboo rhizome root was similar. The volume for D=1-2 mm diameter class was the biggest (50.78%). There were significant differences between the rhizome growth stages of tensile strength and modulus strength for both Moso bamboo and Lei bamboo. The tensile strength of middle-aged rhizome was obvious higher than that of young and old aged rhizome, while the modulus strength of middle-aged rhizome was significant lower than that of young and old aged rhizome. It showed that the growth stage was a factor influencing the biomechanical properties of Moso bamboo and Lei bamboo. The relationship between tensile strength and diameter of Moso bamboo and Lei bamboo root systems were both in negative power function with the saturated moisture content, and that of Moso bamboo basal root and Lei bamboo rhizome root were still in negative power function with 12% moisture content. However, the relationship between tensile strength and diameter of Moso bamboo rhizome root and Lei bamboo basal root were not significant any more. The relationship between shear strength and dry matter quality of underground systems of Moso bamboo and Lei bamboo were both in power function, and the increasing trend of shear strength for Moso bamboo was higher than that of Lei bamboo.