In conventional design of soil-nailed slope, the nail parameters such as nail spacing (1–2 m), and nail inclination (10º–20º) have been recommended without considering any specific slope angle. Henceforth, this paper presents a numerical evaluation on the soil-nailed slope with flexible facing based on the finite element method in order to investigate the range of those two parameters with any size of nail head in various slope angles (45º, 55º, 65º, and 75º). Based on a minimum factor of safety (FS_min = 1.5), the analysis results indicated that the suggested range of those parameters in the conventional specification was applicable in the slope angle of 45º and 55º with any sizes of nail head. Nevertheless, it was not practical for slope angle of 65º and 75º, which required the size of nail head at least 400 × 400 × 250 mm, with nail spacing less than or equal to 1.5 m, and nail inclination from 5º to 10º.