The invention discloses a device for guaranteeing horizontalness of a dowel bar on a concrete pavement. The device comprises a positioning rack, dowel bars, sleeves sleeved on the outer sides of the dowel bars, and positioning mechanisms for positioning the dowel bars and the sleeves, wherein the positioning rack comprises a bottom plate and a coaming which is fixedly connected with the bottom plate; the bottom plate and the coaming are matched to form a groove; multiple guide through holes are uniformly distributed in the bottom plate; the positioning mechanism comprises multiple bosses which are uniformly distributed in the groove and are fixedly connected with the bottom plate; a positioning plate is arranged in front of the boss; clamping assemblies are arranged on the bosses and the positioning plate. The invention also discloses a using method of the device for guaranteeing horizontalness of the dowel bars on the concrete pavement. The using method comprises an assembling step and a disassembling step. The device is simple in structure and convenient and reliable to operate, the horizontalness of the dowel bars and the distance between the dowel bars can be guaranteed, the bearing performance of the concrete pavement is improved, and the service life of the concrete pavement is prolonged.