Abstract: The steam turbine is one of the most important rotation equipments in the Nuclear Power Plant, the blade of steam turbine is likely to engender crack in the root position that may eventually affect the safety work of low-pressure rotor. The article mainly introduces ultrasonic inspection methods concerning the fir type blade of steam turbine. It is helpful to master the method on how to judge the defects according to the inspection technique of blade root that we researched. The inspection result indicated that the technique researched has good application effectiveness, and the development of the ultrasonic inspection technique of blade root has great significance in the area of assuring the safety and reliability running condition of steam turbine.