The effect of DH on the electrochemical property and oxide film of Alloy 182 in simulated primary water has been studied by in situ CER and EIS measurements and ex situ SEM, XPS and Rarnan spectroscopy.Both CER and EIS results indicate film resistance (Rfilin) increases with decreasing DH and the increase is slight in Ni stable region while after exposed in NiO stable region the Rfilm increases sharply.In the last stage of the test the DH was switched back to 50 cc/kg.CER decreases gradually in the last two days while the resistance is still higher than that in the initial stage with the same DH.In DH=50 cc/kg and 30 cc/kg conditions, the oxide film is very thin and mainly consists of Cr2O3.Ni exists in the form of Ni(OH)2 and spinel in the outmost layer.In DH=5 cc/kg conditions the oxide film grows much thicker and the outer part is mainly NiO and spinel while Cr2O3 mainly locates in the inner part.After switching back to DH=50 cc/kg condition, The film thickness decreases significantly and the reduction mainly happened in the outer NiO-dominated part.The concentration of the Cr2O3 which is enriched in the inner part increases correspondingly.The SCC susceptibility of Alloy 182 is mainly decided by Ni oxidative dissolution in Ni stable region.Decreasing DH leads the oxidative dissolution reaction to forward direction accompanying with an increase of the Ni2+ ion solubility.Although Cr2O3 can form in these conditions and resistance increases with decreasing DH, because of the low amount of Cr (15 wt%) the Cr2O3 cannot fully protect the substrate against dissolution.Further decreasing DH makes the specimen traverse Ni/NiO phase boundary and stabilize as NiO considering the fact that NiO solubility is smaller than the Ni2+ ion solubility in such conditions.The formation of NiO can increase the film resistance as indicated by CER and EIS results, which can in turn act as a barrier for the ions diffusion and protect the substrate against further dissolution.This can explain why SCC susceptibility decreases in NiO region.