Abstract: Reinforcement vertical spacing is one of the key technical parameters affecting the performance of geosynthetic-reinforced soil structures. Based on the upper-bound theorem of plastic limit analysis and the pseudo-static method, this study derives the external power and internal energy dissipation rate of opposed-wrap reinforced embankments under combined action of strip surcharge and seismic forces. By incorporating the shear strength reduction method, the rational vertical reinforcement spacing for embankment stability is determined. For the case study in this paper, the maximum vertical spacing of reinforcements to ensure embankment stability should not exceed 0.50 m. Furthermore, the main factors influencing embankment stability and reinforcement spacing are thoroughly analyzed to investigate their variation patterns and mechanisms affecting reinforcement spacing. The results demonstrate that the allowable reinforcement spacing increases with the enhancement of reinforcement strength, soil cohesion, and internal friction angle. Conversely, the required spacing decreases progressively with increasing soil unit weight, surcharge load, and seismic coefficient.