Abstract: The martensitic heat-resistant steel is a structure material usually in thermoelectricity industry. Based on characteristic of different engineering projects, different welding technologies are needed because the material is susceptible to carck, leading to unvoidable hidden danger to safety in engineering equipment. The method of NDT inspection of welding assembly quality of the material must be used in time. In the same time, main points of ultrasonic testing were introduced and contributing factor of welding defect was analyzed. The results showed that, in order to have welding quality in accordance with engineering demands, the combination of X-ray inspection with ultrasound and penetration testing and with other means of nondestructive testing is needed to decrease rate of undetected fault.