The invention relates to a treatment method for rural sewage based on three-grid septic tank, belonging to the technical field of sewage treatment. The treatment method comprises the following steps of: modifying the three-grid septic tank and arranging a water-collecting well; arranging an enhanced anaerobic barrel for carrying out deep anaerobic treatment to the discharged water of the three-grid septic tank; and jointing the anaerobic barrel and a biological filter. The monitoring result of water quality treated by the method shows that the discharged water reaches national one-level B discharge standard.