Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na_2MoO_4 for carbon steel,which is studied in 55%LiBr+0.07mol/L LiOH solution at high temperature.Testing results indicate that the passive film on carbon steel surface is mainly composed of Fe_3O_4,and Mo is involved in the process of film forming,in a form of MoO_3 and MoO_2.The parametric analysis of the evolving potential and the blend potential of MoO_2 shows that Mo mainly exists as MoO_2 in passive film when the concentration of Na_2MoO_4 is lower than 150 mg/L.While its concentration is greater than 150mg/L,it mainly exists as MoO_3 inside the film and exists as MoO_2 outside the film.MoO_4~(2-) is deoxidized as MoO_2 on the surface of carbon steel,which may impede the corrosion of active-site and raise the blend potential of carbon steel,and then MoO_4~(2-) adsorbs onto the defects of the passive film and decompounds as MoO_3 during the process of film forming.The electric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution.As a result,heavy concentrated Na_2MoO_4 solution(greater than 150mg/L)has excellent inhibition effect on carbon steel in LiBr solution. Electrochemical measurement and chemical immersion test are employed to investigate the inhibition mechanism of Na_2MoO_4 for carbon steel, which is studied in 55% LiBr + 0.07 mol / L LiOH solution at high temperature. TEST RESULTS indicate that the passive film on carbon steel surface is mainly composed of Fe 3 O 4, and Mo is involved in the process of film forming, in a form of MoO 3 and MoO 2. The parametric analysis of the evolving potential and the blend potential of MoO 2 shows that Mo mainly exists as MoO 2 in passive film when the concentration of Na_2MoO_4 is lower than 150 mg / L.While its concentration is greater than 150 mg / L, it mainly exists as MoO_3 inside the film and exists as MoO_2 outside the film. MoO_4 ~ (2-) is deoxidized as MoO_2 on the surface of carbon steel, which may impede the corrosion of active-site and raise the blend potential of carbon steel, and then MoO_4 ~ (2-) adsorbs onto the defects of the passive film and decompounds as MoO_3 during the process of film forming.The e lectric field caused by different valence of Mo in passive film may retard the dissolution of carbon steel and lead to an increase in the polarization impedance and a decrease in hydrogen evolution. As a result, heavy concentrated Na_2MoO_4 solution (greater than 150 mg / L) has excellent inhibition effect on carbon steel in LiBr solution.