The invention discloses a coating device for spraying for a petroleum casing pipe. The device comprises nozzles I, nozzles II and a conveying pipeline; a spraying ring is arranged between the nozzles I and the conveying pipeline and is hollow; spraying holes I are formed in the outer side surface of the spraying ring; the nozzles I are connected with the spraying holes I; paint inlets I are formed in the inner side surface of the spraying ring; the conveying pipeline communicates with the paint inlets I; a fixing ring is arranged between the nozzles II and the conveying pipeline and is hollow; spraying holes II are formed in the inner side surface of the fixing ring; the nozzles II are connected with the spraying holes II; paint inlets II are formed in the outer side surface of the fixing ring; and the conveying pipeline is connected with the paint inlets II. Paint is sprayed onto the inner wall of the casing pipe through the nozzles I, and the paint is ejected onto the outer wall of the casing pipe through the nozzles II. With the spraying device, no paint pool is required to be built, so that the conditions that the paint is exposed to the air for a long time, impurities are doped are avoided, the quality of the coating layer of the casing pipe is improved, and the cost is reduced.