Abstract: The effect of Cl^- concentration on the electrochemical corrosion behavior of SiC_P/Al composites was inverstigated by using immersion test, electrochemical polarization and electrochemical impedance spectroscopy test technique. The results show that passivation is not obvious of SiC_P/Al composites in Cl^- medium and the corrosion process is mainly pitting corrosion. With increasing of Cl^- concentration, the corrosion rate of SiC_P/Al composites increases, the pitting potential decreases, and the corrosion mechanism of the composites presents the characteristics of transfering from a unique charge transfer process mechanism to a mixed mechanism control of charge transfer process and corrosion production diffusion. Electrochemical impedance spectroscopy exhibits two type with increasing of Cl^- concentration:a unique capacitance arcs type and a mixed type including a capacitance arcs in high frequency region and a straight line with the real axis of 45° (classics Warburg resistance) in low frequency.