Abstract: Due to long-term operation of tension clamp, the internal sealing material is prone to failure, which results in water accumulation, bulge and corrosion in the unpressed zone, steel core and aluminum tube breakage, and finally to cause serious power accidents. A method to detect water ingress into the crimp tube based on ultrasonic pulse reflection is proposed.The optimal detection frequency, the best detection position and the echo characteristics of water ingress are studied. The results show that for the primary echo at the inner surface of the aluminum tube: the echo peak in the case of water ingress is less than that in the case of air; and the echo amplitude remains unchanged while the water accumulation depth changing. By observing the arriving time of the primary echo at the water-air interface, the water depth inside the crimp tube can be evaluated. This method provides a new idea for detecting the water ingress into crimp tube.