Abstract: The capacitor discharge spot welding of the Al₂O₃ fiber reinforced Al-matrix composites was conducted.In the welded joint, the microstructure has a well transition from matrix to nugget, and the small quantity of Al₂O₃ fiber are broken down due to the effect of electrode force, which distributes in periphery of the nugget. Due to very short time in welding, the cooling rate of the joint reaches to 10⁶ K/s, and the microstructure of the nugget is obviously characterized by rapidly solidified microstructure.The segregation of alloy elements in the alloy phase decreases.The solid solubility of Si atoms in the α-Al is increased.The eutectic transformation is suppressed, and the microstructure of nugget refines remarkably.Under the heat cycle, because of the different coefficient of thermal expansion between Al₂O₃ fiber and α-Al matrix, the interface of Al₂O_3F ADC12 becomes potential crack source.