The invention discloses an efficient wall-whitewashing scraper knife comprising a scraper knife blade and a handle. The handle is fixedly arranged at the top end of the scraper knife blade; the two edge sides of the scraper knife blade are welded to one sides of a first box body and a second box body correspondingly; and a metal elastic piece is arranged between a second telescopic rod and a thirdtelescopic rod. According to the efficient wall-whitewashing scraper knife, the first box body and the second box body are fixedly arranged on the two edge sides of the scraper knife blade, the second telescopic rod and the third telescopic rod are arranged in the first box body and the second box body correspondingly, and the bottom ends of the second telescopic rod and the third telescopic rodare both connected with brush plates through rotating pieces so that the first box body and the second box body can be opened manually; the lengths of the second telescopic rod and the third telescopic rod are adjusted through the metal elastic piece, and then the connecting pieces are rotated so that the brush plates in the box bodies can whitewash a wall body; and a first telescopic rod is mounted in the handle so that the scraper knife can extend, namely, the situation that the wall body is polished or whitewashed through an outside tool is not needed, and the efficiency of workers is improved.