Abstract: Replacement of fresh water with sea water is an effective way to save time and cost in a water pressure test. 08MnNiVR tank steel is a kind of important steel material newly developed for large-scale tank, but its feasibility in a seawater pressure test has not been verified yet. This paper studies corrosion resistance performance of 08MnNiVR tank steel in sea water and fresh water by means of electrochemical test, soaking test and slow strain rate tension (SSRT) test, highlights the comparison of corrosion performance difference in sea water and fresh water, providing experimental basis and data support for a seawater pressure test of 08MnNiVR storage tank. The study results show that 08MnNiVR storage tank, if immersed in sea water and in fresh water separately, has very similar corrosion currents, basically consistent free corrosion potential change trends, approximate corrosion rates and low stress corrosion cracking susceptibility. It is indicated that 08MnNiVR tank steel has very similar anti-corrosivity performance in sea water and fresh water, laying experimental base for a seawater pressure test.