Abstract: The bent section of the austenitic stainless steel small diameter pipe of the boiler is susceptible to stress corrosion cracking and leakage. For ultrasonic testing, there are technical difficulties such as coarse grains, small contact surfaces and large curvature. Taking the detection of the inner wall of the bent pipe of a screen superheater in a thermal power plant as an example, the specific detection process could only be determined through the design and selection of the detection probe, the design and manufacture of the reference test block, and the determination of sensitivity and the evaluation method. The comparison between actual test results and physical anatomy shows that the test method can effectively detect cracks on the inner wall of the austenitic steel small diameter pipe bend.