In the present research, changes in surface physic-chemical structure of UHMCFs during the electrochemical surface oxidation with increasing current density were studied by scanning electron microscopy(SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy (Raman),respectively. The mechanical properties of UHMCF and the interlaminar shear strength (ILSS) of UHMCF reinforced epoxy (EP) composites before and after the electrochemical oxidation were also researched. Based on the test results, a step-wise oxidation mechanism ofUHMCFs in the electrochemical modification was proposed.