A method of ultrasonic brazing metal matrix composite, which forms a reinforced composite bond without filling welding wire with reinforcement or adding alloy element to generate ceramic phase, includes the steps of setting a filler metal; introducing ultrasonic vibration to braze in air; dissolving the base materials, and introducing ultrasonic wave again. The method performs the aluminum brazing at low temperature. The periodic time of brazing is shorter and the cost is lower than the conventional brazing methods. The strength, service temperature and dimensional stability of the joint are close to the base article.