Abstract: A new type of martensite heat-resisting steel T92 was introduced in 1 000 MW ultra-supercritical units, whose alloy element content was higher than former boiler steel. T92 steel is susceptible to welding cold cracks, imposing serious harmfulness on the unit operation. Therefore, the higher detection rate of crack is requested for X-ray testing technology. This paper showed some test results for satisfying a higher demand for radiation detection of cracks, put forward X-ray inspection technology for thick walled T92 steel welding joint. Field inspection confirmed that the technology met the requirement.