Abstract: 10CrCuSiV was a new kind of low alloy steel for resistance Sea-corrosion,its corrosion rate was 0.23 mm/a in the sea after immersed 7 years.Used the metallograph,lithofacies-MIC, X-ray diffraction, SEM and electron energy spectrum etc, the results are shown:1) The rust on the 10CrCuSiV steel has strong adhesive power, compact texture and small adhesiveness coefficient. 2) In-surface rust of the 10CrCuSiV consists of the Fe₃O₄ mainly and has better protection. 3) The alloying elements (Cr, Cu, Si etc.) are collected in the rusy pit,so the local corrosion is controlled effectively.