Abstract: In order to clean up corrosion deposits in the blowdown cave of secondary side of steam generators in Unit 1&2 of Tianwan nuclear power station and reduce its corrosion risk to base metal of shell and weld joints, a hydraulic flushing device was developed and applied during the outages. Through hydraulic flushing, the corrosion products accumulated in the blowdown cave of steam generators for more than ten years were cleared. The inside walls of the blowdown cave and the weld joints were checked and they are in good condition, which improved the operational safety and reliability of the steam generators.