Root-reinforced soil is treated as composite material, with mechanical root-soil interactions enhancing soil strength upon shearing; however, its reinforcing effect decreases over time due to plant senescence and root decay. Soil density, influenced by compaction that arranges particles and reduces pore space, determines the soil’s ability to support root networks and root-soil interaction. The effect of root network and root decay on shearing behavior relating to difference in soil density remains unclear. In this study, vetiver roots were used to conduct two series of undrained triaxial tests with root decay periods of 45 and 90 days to investigate the shear behavior of root-reinforced soil. The vetiver root volume fixed with 0.74% of total volume of specimen. Two different root networks have been installed with vertical root and vertical-horizontal root segments following compaction density of 1.23 Mg/m³ and 1.46 Mg/m³. The compaction density of 1.23 Mg/m³ has been used to investigate the effects of root orientation and network by installing vertical root and vertical-horizontal root segments with the same volume. Moreover, compaction density of 1.23 Mg/m³ and 1.46 Mg/m³ have been prepared for proving the ability of root-soil interaction on the different soil density by installing the same condition of roots orientation (vertical-horizontal) and volume. Finally, the shear behaviors with different root conditions were compared. Vertical root segments had higher at peak shear strength, but lower shear strength at 15% axial strain compared to vertical-horizontal root segments. Moreover, roots in loose soil resist against shearing better than those in dense soil.