Abstract: The effect of HEDP on corrosion behavior of 1Cr18Ni9Ti in HNO3 cleaning system (10% HNO3,50 ℃) was studied by electrochemical testing,metallographic and electronic scanning probe observation.The results showed that the pitting resistance of 1Cr18Ni9Ti was further improved by adding HEDP to HNO3 system.The synergistic effet between HNO3 and HEDP′s secondary passivation would promote the repair of passivation film of 1Cr18Ni9Ti damaged in HNO3 system.