The invention relates to the field of surface treatment, and particularly discloses a spraying method for a coating on the inner wall of a pipeline. According to the spraying method, a magnetic spraying device is adopted, and a coating device in the magnetic spraying device is placed in the pipeline; a first magnet mounted on a driven gear can attract a second magnet, a connecting rod connected with the second magnet is pulled at the same time, a sliding block is made to move in a branch pipe, a discharging port between the branch pipe and a corrugated pipe is not blocked any more in the moving process of the sliding block, and paint in a paint storage box can flow into a storage cavity of the second magnet accordingly; and when the driven gear rotates, the second magnet is driven to rotate at the same time, the whole coating device is made to rotate accordingly, paint in the coating device flows out from a spraying port of the second magnet under the effect of centrifugal force in the rotating process and then is sprayed onto the inner wall of the pipeline, and the inner wall of the pipeline is coated. By adoption of the scheme, the inner wall of the pipeline can be sprayed.