Abstract: The interface-regulating mechanisms of atmospheric air plasma modification for ultra high molecular weight polyethylene (UHMWPE) fiber/epoxy composites were investigated from the perspective of engineering application. The influence of plasma treatment duration on UHMWPE fiber surface properties and the interfacial adhesion of UHMWPE/epoxy composites was mainly researched. The SEM and surface water absorption tests were chosen as characterization methods to study the effects on UHMWPE fiber surface morphologies and surface wettability, respectively. Furthermore, the UHMWPE/epoxy composite interfacial adhesion was characterized based on both of the fiber surface adhesion test and the interlaminar shear strength test of laminates by using the stretching load and the bending load, respectively. The results show that the UHMWPE fiber surface adhesion is increased by 84.0% after plasma treatment for only 4 s, and specially the interlaminar shear strength value of UHMWPE/epoxy composite laminates is increased from 7.01 MPa to 15.81 MPa with the increment of 125.5%. These results indicate that the interfacial properties of UHMWPE/epoxy composites can be regulated notably and effectively by UHMWPE fiber surface air-plasma treatment, providing a theoretical basis for its subsequent expanded engineering application.