The front surface (FS) specimen and side surface (SS) specimen of CF8611/AC531 composite and the electrolyte with 3.5% NaCl+12.5% Cu2SO4 are designed. With the electrochemical workstation, scanning electron microscope, scanning vibrating electrode and other equipment, the electrochemical measurement of CF8611/AC531 composite and 7B04-T74 aluminum alloy and the immersion test of the coupling specimens are carried out. After soaking in the 35 ℃,3.5% NaCl electrolyte for 0 h and 96 h, the self-corrosion potential and self-corrosion current density of FS are 96 and 117 mV, 1.742×10-7and 2.213×10-7 A/cm2, and those of the aluminum alloy are -870 and -897 mV, 2.920×10-5 and 3.068×10-5A/cm2, respectively. The polarization current densities of FS and SS specimens in the 35 ℃, 3.5% NaCl + 12.5% Cu2SO4 electrolyte are 3.99×10-4 and 1.01×10-3A/cm2 separately, and the Cu metal is obviously deposited on the exposed carbon fiber. In the 35 ℃,3.5% NaCl electrolyte, the galvanic current density of FS/7B04 is 6.75×10-6 A/cm2 and it is less than that of SS/7B04 with 6.2×10-5 A/cm2. The results show that, the electrochemical property of the composite is stable. The electrochemical activity of FS specimen is lower than that of SS specimen. The contribution of the exposed carbon fiber in the electrochemical response of the composite is proved. There are some exposed carbon fiber defects on its original surface and it is divided into the active cathode area and the inert cathode area. The main corrosion form of the aluminum alloy in coupling specimens is pitting, accompanied by a small amount of trenching form. The occurrence mechanism and development pathway of trenching corrosion are revealed. The galvanic effect of SS specimen on the aluminum alloy is significant than that of FS specimen. No evidence of degradation of the composite is revealed and the reason is discussed. The cathode site on the surface and the hydrolysis of Al3+ could weaken the galvanic effect.