As a result of technological advances, geosynthetic reinforced soil (GRS) slopes have been constructed more frequently in recent decades, which have been used extensively in landslide stabilization, highway construction, and geological disaster prevention. A new formula was developed for predicting the probabilistic sliding displacement of GRS slopes in this paper. An example of a model based on numerical simulation (Slide) was illustrated to calculate seismic displacement based on three types of Newmark analysis. A synthetic dataset including 972 numerical simulations was generated for statistical analysis by data derived from real-time strong-ground motions of 30 worldwide earthquakes. An investigation into the relationship between reinforced slope properties and motion characteristics was performed using a parametric analysis. It was concluded that coupled analysis calculated higher values for earthquake-induced sliding displacement of GRS slope. Also, statistical analysis indicated that soil friction angle is more influential on sliding displacement than the other random variables. A cumulative distribution function was constructed for estimating probabilistic seismic displacement based on 5000 Latin-hypercube sampling.