The invention discloses an adjustable trowel which comprises a base. A trowel body is fixedly installed on one side of the base. A supporting block is fixedly installed at the top end of the base. The upper portion of the supporting block is in seamless connection with one end of a transverse rod. The interior of the transverse rod is hollow. An inner rod is arranged inside the transverse rod. The inner rod is in a test tube type. A gear is arranged at the other end of the interior of the transverse rod and meshed with teeth arranged on the inner rod. A through groove is formed below the gear and in the transverse rod. A second groove is formed in the end, away from the through groove, of the transverse rod. A first groove is formed in one side of the inner rod. The bottom end of a supporting device arranged inside the first groove is hinged to the inner rod through a bolt. The inner rod is pulled out from the transverse rod through a pulling bridle, the length can be adjusted, operation can be conveniently performed on a wall or a high place, a first supporting rod, a second supporting rod, the transverse rod and the inner rod form a triangle, the structure is more stable, and operation can be performed conveniently on a wall crown or a high place.