A novel sensor for ocean electric field testing has been fabricated by polyacrylonitrile-based on carbon fibers with electro-chemical oxidation. The surface profile characteristics of the carbon fibers were characterized by scanning electron microscope, Fourier transform infrared spectra and contact angle. Cyclic voltammetry and Tafel curves have been used to study its electrochemical performances. Two identical electrodes in sea water as the electric field sensor will swiftly respond to applied electric field which causes positive and negative ions to move in opposite direction, resulting in a electric potential difference (ΔE). Test result indicates that the offset potential is typically below 1 mV with a drift of 60–170 µV d –1. Typical self noise level is 1.07 nV/√Hz@1Hz . The electric field response indicates that the modified electrode pair shows better response to AC sine signal of amplitude and frequency (5 mV and 1 mHz) respectively than its blank. The electric field response model of the modified electrodes is creatively presented according to its electric double layer capacitance and Faraday pseudo-capacitance. Many advantages of the carbon fiber electric field electrode will make it have potential application prospect.