Abstract: In recent years, it is required to inspect the expanding area of steam generator tubes in nuclear power plants. There is a blind area for conventional eddy current testing with Bobbing probes in the expanding area, so immersion ultrasonic testing from the inside of the tubes was developed. The experiment results showed that, the immersion ultrasonic testing can meet the need of inspection for expanding area of steam generator tubes. The immersion ultrasonic inspection can be a supplement of eddy current inspection, and at the same time, it can be applied in other thin-wall and small diameter tubes.