Abstract: In order to study CI- and SO42- in the liquid preparation water affected to the corrosion behavior of the high water content hydraulic fluid, an electrochem cal polarization curve was applied to study the corrosion behavior of high water content hydraulic fluid with different CI and SO42- density and discussed the mechanis m affected to the corrosion behavior of the high water content hydraulic fluid.The results showed that with the CI and SO42- density increased, the pitting potential of 3 0 Cr Mn Si material would be decreased and the corrosion resistance performances of the high water content hydraulic fluid would be reduced.When the CI- in the liquid was increased from 0 to 200mg/L, the pitting potential was decreased by 43%.When the SO42- in the liquid was increased from 0 to 400 mg/L, the pitting potential was decreased by 17%.The pitting potential and the CI and SO42- density would be in a linear relationship.The main mechanism affected to the corrosion resistance perfor mances of the high water content hydraulic fluid would be the competitive adsorption of the anions.In the selection of the corrosion inhibitor and the application of the hi gh water content hydraulic fluid, a corrosion inhibitor affected to anti CI and SO42- should be both selected in order to ensure the corrosion resistance performances of the high water content hydraulic fluid.