Abstract: In this paper, the carbon fiber of high strength and middle modulus was studied. Mechanical properties and surface activity characteristics of high strength and middle modulus, and its effect on the interlaminar stear strength (ILSS) of composites material were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and dynamic contact angle instrument. It is found that current density has remarkable effects on fiber surface element content, -OH, -C=O and -COOH functional group content and polar free energy. When current density increases to 0.23 mA/cm², the polar free energy of carbon fiber reaches the maximum value of 5.5 m/Nm, and the ILSS reaches 111 MPa, which increase by 10 times and 68.2%, respectively, as compared to untreated fibers.