In this study, the influence of modifying ZnO filler with surface-treating agents on the thermal conductivity of the ethylene-vinyl acetate copolymer (EVA) composites was reported. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were applied to analyze the surface modification of ZnO filler and the fractured surface morphology of the EVA-ZnO composites. The test results indicated that surface-treating ZnO filler with the valid modifying agents (stearic acid, OL-AT16, KH-560, or NDZ-132) at right dosage and treating temperature, the thermal conductivity of the EVA-ZnO composites can be enhanced effectively on account of reducing the interfacial phonon scattering; while the dosage of modifying agents exceed a right amount, the thermal conductivity of EVA-ZnO composites modified with the small-molecule treating agents (F-1, n-Octylic acid, or stearic acid) descend more evidently with the dosage increase.