A numerical model was established for the widening of a road embankment subjected to long-term asymmetric traffic loading in Shanxi Province, China. The model was created using FLAC^3D software, with traffic load simplified to half-sine wave. The geogrid was simulated by FLAC^3D structural element, and the soil was modeled by solid element. Mohr-Coulomb criterion was used to estimate the failure of geogrid and soil. The deformation and stability of both unreinforced and reinforced embankment widening under asymmetric traffic load were analyzed. Furthermore, parametric study was conducted to investigate the deformation of reinforced widening embankment under different parameters including:fill properties of the widening embankment, amplitude and frequency of traffic load, and running interval. The results show that the deformation of the widened embankment is only partially restricted by the geogrid, while the global stability of the embankment under asymmetric traffic load is effectively improved. Differential settlement decreases as the fill properties of the widening embankment increases. Through comparative analysis, it was found that the effect of cohesion on the differential settlement is more obvious than that of the compression modulus. Smaller differential settlement can be obtained when the soil properties of the new and old embankments are similar. In practical engineering use, by ensuring the properties of new embankment fill are the same as those of the old embankment fill, differential settlement can be effectively controlled under dynamic load situations, and will not affect the comfort and safety of the vehicle. The increase in amplitude of traffic load only on one side of the embankment will lead to excessive differential settlement and the pavement smoothness will be seriously affected. As the frequency of asymmetric traffic load and running interval increases, embankment settlements gradually decrease, while the differential settlement will remain constant. The findings in this investigation can provide a theoretical basis for the construction of the widening embankment under asymmetric traffic load.