The expansion joints of diversion penstocks for Three Gorges Hydropower Station are of the biggest ones with telescopic water seal corrugated pipe in China at present. The fabricating accuracy requirements are very high. In order to verify the fabricating quality and the design strength of the expansion joint as well the sealing ability of the corrugated pipe and water seal

the water pressure test must be done. The paper introduces the technique and process of the water pressure test.