Abstract: While applying conventional ultrasound tests method to detect the rail joint of aluminum-thermic welding, for different detecting regions, it is needed to use different K property of probes, also, it is hard to detect the flaws of light spot and gray spot for the reason of signal reflecting, so utilizing focus and deflect of ultrasonic phased array to overcome conventional ultrasound tests method inadequacy. Through detecting rail joint of aluminum-thermic welding with nature and machining flaws, the effectiveness of ultrasonic phased array method was validated as compared with results of conventional ultrasound test. The experiment results showed the ultrasonic phased array inspection for rail joint of aluminum-thermic had fast detection speed and high efficiency; the result could be shown visually and reproducible.