<p>Ecological engineering measures are widely adopted to reinforce soil, mitigating erosion, landslides, and other geological hazards, while also preventing engineering failures, such as slope collapses and road embankment instability. Previous studies have demonstrated that plant roots significantly enhance soil strength and play a critical role in soil stabilization. This study aims to investigate the dynamic response of root-reinforced soil induced by traffic loading through dynamic triaxial tests. The experiments employ typical slope protection plants (<i>Pyracantha fortuneana L.</i>) and loess from northern China. The experimental design quantifies the contribution of root distribution patterns to soil reinforcement by manipulating vertical and horizontal root ratios in orthogonal patterns. The proportion of vertical roots in total root mass is controlled at 100%, 75%, 50%, 25%, and 0%. Root presence significantly enhances both liquefaction resistance and deformation resistance, with a strong correlation observed between reinforcement effects and vertical-to-horizontal root ratios. Among these ratios, the arrangement with 25% vertical root mass exhibits optimal resistance against liquefaction and deformation, showing a reduction in maximum elastic strain by up to 50.26% and plastic cumulative deformation by over 100% compared with the 100% vertical root configuration. This demonstrates that an appropriate balance between vertical and horizontal roots effectively enhances soil stability under cyclic loading conditions. Furthermore, dynamic constitutive and cumulative plastic deformation models were developed specifically for root-reinforced soil by introducing an exponential coefficient <i>C</i>, related to the vertical-to-horizontal root ratio <i>P</i>, based on the Hardin-Drnevich model. These findings highlight the existence of an optimal root distribution pattern that governs both the liquefaction resistance and dynamic behavior of root-reinforced soil.</p>