Abstract: Dissimilar metal connectors are special threaded brazed structures of dissimilar metals, featuring a large tube sleeving a small tube. The large tube is made of stainless steel, and the small tube is made of titanium alloy. The tubes are connected by threads and then brazed. When ultrasonic methods are used to inspect the welding quality, traditional manual ultrasonic testing suffers from poor stability, low efficiency, non-intuitive results, and large defect measurement errors due to the influence of dissimilar metals and the threaded structure. Based on the basic principles of water immersion contact ultrasonic testing, research on automatic ultrasonic testing technology for dissimilar metal connectors was conducted. Key technologies such as adaptive coupling of probes and automatic supply of coupling agents were breakthrough, and an automatic ultrasonic testing device for dissimilar metal connectors based on the water immersion contact method was developed, combining automatic scanning and signal acquisition processing. Relevant verification tests were carried out. Test results showed that the automatic ultrasonic testing technology based on the water immersion contact method improved the detection reliability, stability, and efficiency of dissimilar metal connectors.