The effect of diameter, chirality and volume fraction of SWCNTs on the tensile behavior of nanocomposites is studied. Multi-scale material modeling is applied to assemble different RVEs composed of various SWCNTs embedded in polymer. Nanotubes are modeled in continuum mechanics, based on their atomic structures as space frame structures. Beam elements in this structure are defined based on carbon bonds characteristics in molecular mechanics. Polymer portion of the RVE is modeled as a linear elastic continuum material, with lower accuracy regarding to the multi-scale modeling technique. Attained stress-strain curves obtained from modeled nanocomposites revealed that using Armchair SWCNTs in RVEs makes nanocomposites tougher rather than Zigzags. Also, diameter of CNT has an inverse effect on the curves level. Moreover, the effect of diameter is more obvious at higher volume fraction of CNTs.