Adding carbon nanotubes (CNTs) to polymer composites for increasing strength and toughness has become a usual approach nowadays. In this dissertation, the effect of adding CNT on properties such as strength, toughness, and ultimately the impact of agglomeration of the particles on these properties are investigated using FEM in Abaqus. In this approach, by selecting RVE consisting of the epoxy matrix and carbon nanotubes, the effect of carbon nanotubes and agglomeration is modeled. The Brittle cracking model is chosen for the polymeric matrix to investigate the composite’s strength in the model. Also, due to the significant the effect of interface properties of CNTs and the matrix on the composite’s ultimate strength, the interface properties are used as additional input for the model using a cohesive surface with mixed-mode damage behavior. The results show that adding CNTs to the polymeric matrix with aligned orientation can increase the model’s strength up to 10 percent. Also, reinforcing with a 2 percent weight fraction of CNTs, shows a 50 percent increase in the composite’s elastic modulus. In the model, the agglomerated CNTs are in placed in the orientation of the RVE. It is observed that having 50% agglomeration in the composite with 2% CNT can decrease the tensile strength up to 10%. Keywords : epoxy nanocamposite, carbon nanotube, strength, brittle cracking, agglomeration