Abstract: Ultra-high molecular weight polyethylene (UHMWPE) fiber reinforced thermoplastic resin matrix composites for ballistic application were selected as the research object. Composite laminates with unidirectional orthogonal structure were prepared by hot pressing process. Based on the self-designed tensile test device, the in-plane tensile tests of UHMWPE fiber reinforced thermoplastic resin matrix composite on macro and quasi meso scales were carried out to investigate its in-plane tensile mechanical properties and failure modes. The results show that the in-plane tensile mechanical properties of UHMWPE composites for ballistic application on quasi meso scale are their intrinsic properties. With the increase of off-axis angle, the tensile fracture strength decreases exponentially. This is attributed to the failure mode changing from the tensile fracture failure of fiber to the interfacial failure between the fiber and resin matrix. Furthermore, the tensile failure strength of UHMWPE fiber reinforced thermoplastic resin matrix composites on the macro scale is 50.52% lower than that on the quasi-meso scale, because the in-plane tensile mechanical response on the macro scale is the coupling result of in-plane tensile deformation and interlayer delamination failure, that is, the lamination effect of laminates.