The corrosion behavior of oil well tubing P110 steel in environments of different oil-water mixing ratios (0.5:9.5, 1:9, 2:8, quality ratios) in the presence of sulfate-reducing bacteria (SRB) and iron-oxidizing bacteria (IOB) were investigated via biological culture technology, weightlessness measurement, surface analysis and electrochemical testing. The results showed that the corrosion rate of P110 steel is maximum (0.2787 ± 0.0042) at an oil-water ratio of 2:8, while the steel is suffered from heavy corrosion in environments of different oil-water ratio. This is due to that the increase in oil content may lead to an increase in the carbon source, which is in favor of the formation corrosive substances and the growth of bacteria in the solution. After adding ternary compound biocides, the corrosion rate of P110 steel in environments of different oil-water ratio were significantly reduced, especially for the corrosion test in environment of the oil-water ratio of 2:8 for different times, its bactericidal rate of SRB and IOB were above 93% and 85%, respectively with corrosion inhibition rate between 38.08% and 64.11%. In fact, the best inhibition effect was achieved by adding the compounded biocides after 3 d of corrosion, indicating that the effect of compounded biocides on slowing down the corrosion of mixed bacteria of P110 steel was extremely significant; this is due to the addition of compound biocides, which containing D-tyrosine can lead to the existing biofilm dispersion, shedding, while changing the cell structure, destroys the concentration environment, and dimethyl sulfoxide as a synergistic penetrant, can accelerate the Tetrakis hydroxymethyl phosphonium sulfate (THPS) into the biofilm, the synergistic effect of the components in the compound biocides accelerates the process of killing the mixed bacteria, inhibiting the P110 steel corrosion.