The utility model discloses a cleaning tool for a flat head hole of a coupling. The cleaning tool comprises a cutter bit and a cutter bar fixedly connected with the cutter bit. The cutter bit comprises a first scraper portion and a second scraper portion, wherein the first scraper portion is provided with an arc-shaped flat blade which can be attached to any arc surface of the flat head hole, and the second scraper portion is provided with a linear flat blade which can be attached to any plane of the flat head hole. Due to the fact that the cutting edge of the arc-shaped flat blade of the first scraper portion makes line contact with the arc surfaces of the flat head hole, impurities on all the arc surfaces in the flat head hole can be rapidly scraped off under the action of repeated scraping; due to the fact that the cutting edge of the linear flat blade of the second scraper portion makes line contact with the planes of the flat head hole, impurities on all the planes in the flat head hole can be rapidly scraped off under the action of repeated scraping. Thus, the cleaning tool can be used for thoroughly cleaning away impurities in the flat head hole of the coupling.