Abstract: Based on TOFD technique detection principle and technical characteristics, and on the analysis of dead zones existing in thick-walled vessel TOFD inspection, this article proposed layered detection methods to reduce the dead zone of inspection. Combined with the theoretical calculations and experimental test results of test block, tiered testing parameters were proposed and optimized. Detection of 150 mm thick weld was guided according to the results of parameter optimization, and test results showed that excessive defect detection rate could be obtained and the nature of defects could be more accurately determined with high accuracy of defect size. So the layered detection parameters design method can be applied to the thick-walled vessel associated testing.