Nitrate addition is a common bio-competitive exclusion(BCE)method to mitigate corrosion in produced water reinjection systems,which can affect microbial community compositions,especially nitrate and sulfate reducing bacteria,but its effectiveness is in controversy.We investigated the influence of nitrate concentrations on EH40 steel corrosion affected by coexistence of Desulfo vibrio vulgaris and Pseudomonas aeruginosa bacteria.Results demonstrate that only mixed bacteria or nitrate had little effect on EH40 steel corrosion,and nitrate could accelerate the corrosion of EH40 steel through the action of microorganisms.The corrosion promotion of nitrate was dependent on its concentrations,which increased from 0 to 5 g/L and decreased from 5 to 50 g/L.These differences were believed to be related to the regulation of nitrate in the growth of bacteria and biofilms.Therefore,care must be taken to BCE method with nitrate when nitrate reducing bacteria with high corrosive activity are present in the environments.