To address the stability of high embankment slopes and investigate the influence of spatial variability of gravel soil on slope stability, this study proposes a simplified reliability analysis method of slope stability. Based on FLAC^3D, a numerical model was developed to simulate slope behavior, and a linear regression-based empirical model was formulated to quantify the relationship between soil pressure and spatial variability indicators (e.g., coefficient of variation and correlation length). By mapping the spatial variability of soil parameters to soil pressure fluctuations, the slope reliability was evaluated through the first-order second-moment method (FOSM). The results demonstrate that the mean value of internal friction angle has a significant effect on the stability of gravel soil embankment slope, whereas the coefficient of variation in this parameter is limited. Furthermore, the correlation length of soil spatial variability shows marginal influence on stability outcomes. The computational model was validated against case study data, demonstrating its applicability for practical slope stability assessments.