In penetration problems, the heterogeneity of the concrete would affect the ballistic responses. The presented paper studied the influence by numerical method. During the analysis, the concrete was defined as “numerical concrete”, which was composed with different size aggregates randomly included in the mortar. In the numerical concrete, the ITZ (interfacial transition zone) was replaced with the connected strength (tensile strength and shear strength). Based on the validation of the mesh, the ballistic responses were studied. From the study, it was concluded that: the randomly-distributed aggregates affected the stress symmetry which changed the missile trace, which couldn’t be alternated by concrete in the homogeneous model, and that the residual velocity of the missile decreased with the increase of the connected strength of the interfaces.