Abstract: The principle of ultrasonic detection of brazed joint is analysed, the ultrasonic testing technology for brazed joint of copper and aluminum middle-sized device clamps for field testing is presented in this paper. Supported by ultrasonic simulation technology, the better test parameters are given. The method can detect three typical area and measure the flaw area accurately. The test proved that the result is accurate and the technology is fast and efficient which can be applied in power grid metal metal supervision.