Abstract: The corrosion behavior of SiC_P/Al composites with different SiC_P sizes (220，140，90，70μm) and different SiC_P volume fractions (42%，49%，55%) was investigated by the alternate immersion test. Mass loss was used to evaluate the corrosion rate. The microstructure of composites was observed by the optical microscope (OM). The phase and surface photography of corrosion products were analyzed by the X-ray diffraction (XRD) and scanning electron microscope (SEM) . Experimental results show that the corrosion resistance of the SiC_P/Al composites decreases with decreasing the particle size in the initial stage of corrosion，but increases with decreasing the particle size in the corrosion latter stage. SiC_P accelerates the nucleation of pit，also interrupts the continuity of the matrix channels，alters the growth way and suppresses the further expansion. The corrosion resistance of the SiC_P/Al composites decreases with the increasing the particle content，of which the main corrosion products are Al₂O₃ and Al_xSO_4y OH_z.