The invention discloses a method for treating micro-nano bubbles of oil extraction sewage in an oil field. The method comprises the steps of: feeding micro-nano bubbles generated by a micro-nano bubbles generator into the place which is distanced from the bottom of a container or a pond at 2-60cm under the oil extraction sewage liquid surface in the oil field; and taking the mineralization range of the oil extraction sewage in the oil field as 5000-60000mg.L-1, the oil content range as 10-200mg.L-1, the suspended matter content range as 1-100mg.L-1, and the ventilation rate as 0.5-4L gas/(L water. hour) to treat for 0.5-10h. The sewage mineralization, the oil content and the suspended matter content treated by the method are obviously reduced, and the viscosity ratio of the polymer (some part of hydrolyzed polyacrylamide) solution prepared by the treated sewage is obviously improved compared with the fore-treatment. The method is simple in technology, is low in cost, does not need to add the other chemical agents, and can avoid the secondary pollution; and the method can be used for preparing a polymer flooding system on the oil field spot, eliminating the environment pollution caused by the oil field sewage, and saving the fresh water resource.