Abstract: The ultrasonic testing system of detecting the welding layer of the controlled valve used in subsea trees was manufactured. The 5 MHz probes were used, producing vertical incident ultrasound, coupled by liquid. Three different detection modes were designed to detect the corresponding specific positions. The coordinates of each location of the three modes were read by the 4-axis encoders. The results of scanning image could visually show the information of defects. The detection results showed that the detection method was able to detect the  3 vertical round holes in the welding layer, which provided a feasible detection method to detect the work piece of the similar shape.