Coarse-grained soil (CGS), as a filler with the characteristics of high bearing capacity but difficult compaction for embankment construction, requires an appropriate thickness of a single compaction layer according to the influence depth of vertical dynamic stress. This paper used a numerical analysis using PFC2D following a scale model test with different particle gradations of compacted CGS fillers by adopting a modified PFWD. The results show that the influence depth is about 50 cm under the maximum impact stress of 0.066 MPa if defined the depth as the maximum stress attenuation to 20%. The compacted CGS filler with dense particle gradation and high strength has a rapid attenuation on vertical dynamic stress. Meanwhile, with the increase of stone content (P5, particle size ≥5 mm), the vertical dynamic stress of compacted CGS is attenuated exponentially. The maximum particle size also affects the attenuation of vertical dynamic stress, which needs further research. The findings support the development of non-destructive devices to inspect the compactness of subgrade construction rapidly.