The invention relates to an iron bacteria culture medium for an oil field sewage treatment system. Oil field sewage contains a certain quantity of bacteria which can generate a certain corrosion effect on equipment and a line pipe, thus the oil field sewage is necessarily sterilized before reinjection is carried out, so that the content of the bacteria reaches the water reinjection requirement; and addition of a bactericide in the oil field sewage is an effective sterilization treatment way, a bacteria culture medium is used in the aspects of the detections of the sterilizing effect of the bactericide and the content of bacteria in reinjection sewage. The iron bacteria culture medium comprises the following substances in parts by weight: 0.024-0.025 part of magnesium sulfate, 0.058-0.06 part of ammonium sulfate, 0.048-0.05 part of potassium dihydrogenphosphate, 0.018-0.02 part of calcium chloride, 0.048-0.05 part of sodium nitrate, 0.68-0.7 part of ammonium ferric citrate, 0.029-0.3 part of 10% sodium hydroxide and 97.9-98.8 parts of deionized water. The iron bacteria culture medium has the advantages of high sensitivity and high accuracy, and can be used for quickly detecting the content of the bacteria in the oil field sewage.