This study comparatively analyzed the behavior of elastic properties by aspect ratio of the ultra-high molecular weight polyethylene (UHMWPE) fibers that are added when creating a composite material of polypropylene and UHMWPE. The volume fraction (VF) of UHMWPE fibers added to polypropylene was fixed at 5%. The elastic properties were lumped for analysis according to the aspect ratio of the UHMWPE fibers oriented on the polypropylene matrix; they were analyzed using the Halpin–Tsai model, which involves a theoretical approach and finite element analysis based on the homogenization method. Finite element analysis was performed for fiber aspect ratios of 0.2 to 30 UHMWPE via the homogenization technique using the ANSYS Material Designer. For theoretical comparison, UHMWPE fiber aspect ratios of 0.2 to 100 were comparatively analyzed using the Halpin–Tsai model. When the aspect ratio of UHMWPE fiber was 0.2, it was calculated as 1518 MPa, and when the aspect ratio was 30, it was 2365 MPa, and it increased by 55.8%. As the aspect ratio increased, E22 and G12 converged to a constant value (1550 MPa). In the future, when the volume fraction of UHMWPE changes from 0 to 50%, a study must be conducted to analyze the predicted behavior of the elastic properties when the aspect ratio of the UHMWPE fiber changes.