Shallow slope failures in vegetated terrain necessitate understanding root-soil interaction, particularly for complex root morphologies like heart-shaped root systems. This study employs discrete element modeling (DEM) to investigate the shear strength of heart-shaped root systems in vegetated slopes. Through calibrated PFC3D simulations of root-soil composites, the influence of shear plane depth (0.25d-0.75d) and root area ratio (RAR: 0.53%-0.92%) was quantified. Results reveal strength reduction at deeper shear plane in the root system, attributed to decreasing RAR and root radius. The shear process exhibits three-stage evolution: initial soil-dominated friction, nonlinear strengthening through root bridging, and oscillatory failure due to rupture of roots. Comparison of shear strength envelopes demonstrate that increasing RAR leads to an increase in cohesion. The study establishes quantitative correlations between stratified root morphology and shear failure modes, advancing understanding of the reinforcement mechanism of root system with complex morphology, providing insights into ecological slope stabilization.