Abstract: Researches were carried out for the technology on welding bead of ultrasonic phased array testing of U rib fillet weld in order to solve the issue of it on the thickness of 8mm on U rib fillet weld, which adopted the method of welding specimen flaw detection by inspecting and observing the precision leads to a conduction of the work in Hong Kong-Zhuhai-Macao Bridge, and the like. This article gets some creativity as below: Firstly, a mathematical model of welding nondestructive as per the flaw characterization of U rib fillet weld was built up, proposing a flaw signal image endpoint read value method based on it. The above mentioned method actually leads to simplify the procedure and improve the precision. Secondly, a method of judgment in U rib fillet weld detection based on error-detecting was proposed, which solved the issue of false negatives or false positives among welding nondestructive testing.