Abstract: To achieve in situ ultrasonic testing for bolts of gas turbine transition section in LNG gas turbine power plant, the structure and stress state of bolt were intensively studied in this paper, and simulation samples were tested. It was found that crosswise crack with longer than or equal to 1mm on the lower surface of bolt hex head could be found by single-straight probe, and crosswise crack on other position could be found by small angle longitudinal wave probe with right angle. Finally it was concluded that bolts of gas turbine transition section could be comprehensively detected by using 5P8×12, 12° small angle longitudinal wave probe and 5P6 single-straight probe.