Abstract: Canopy welds (Ω) in CRDM housing are welded seals joining stainless material and playing an important role in leak-proof for CRDM housing. The paper firstly summarizes and outlines the development of the immersion ultrasonic inspection techniques for canopy welds, and then determines the test parameters such as wave type, probe frequency, wafer dimension and layer thickness , and finally carries out the verification test. And through the test it proves that the technique could meet the test requirements of canopy welds (Ω) in CRDM housing.