Recently due to vast population growth and the urge upon construction of heavy structures and due to the low load capacity of the soil, reinforcement is one of the most common techniques for improving the soil. The concept of soil reinforcement is based on adding some tension resistant elements to the soil to improve its mechanical properties. The reinforcement itself must have high tension strength and endurance in the soil area. The main careterias for designing a foundation in foundation engineering is load capacity and soil meeting meaning that the foundation must be able to safely convey the load to the soil such that the soil meeting does not exceed an exact limit. When the soil under the foundation is weak o when the load is extreme it is possible to reduce the soil compression while increasing the load capacity using the soil reinforcement. So many studies are conducted on the idea of soil reinforcement but firstly these investigations are conducted under static loadings and secondly the results of the investigations conducted on dynamic loading are so scarce and much more investigation must be conducted on this issue. The aim of this study is numerical modelling of the behavior of the foundation based on granular grit soil reinforced with geo grid under oscillating loading and comparing the results with results reported by physical model and also developing a numerical model such that by varying the variables the geo grid reinforced soil load capacity under dynamic and static loadings could be predicted. To conduct the numerical modeling the PFC3D finite element method based software was used. First results of three axis modeling of unreinforced soil under static and dynamic loadings are compared with results of physical model the result of this compare is the proper parameters for finite element modeling. Then modeling the reinforced and unreinforced soil under dynamic cyclic loading is conducted. Again to evaluate the accuracy and precision of the numerical modelling the physical and numerical modeling are compared. The results of modelling and the conducted analysis showed the parameters required for the numerical modeling can be acquired using few experiments. On the other hand the reinforced soil had higher load capacity and deformation capability compare to unreinforced soil. Also in reinforced soils with different levels of geo grid content increasing the depth of geo grid from its optimum level the behavior of the soil gets more similar to unreinforced soil.