Abstract: The Inconel 783 nickel-based alloy bolts of ultra-supercritical thermal power unit have been fractured for many times. In this paper, combined with on-site testing cases, the shape, grain size and sound speed of the bolts are analyzed, and the optimum ultrasonic testing technology is selected and the test were carried out, the results showed that it can effectively detect the bolt crack, and has certain reference significance to the ultrasonic detection of this kind of bolt.