The invention discloses a paint brushing device for the outer wall of a water conservancy pipeline. The paint brushing device comprises a base, an upper clamping block, a lower clamping block and fixing devices. A screw rod is further rotatably mounted on the inner sides of the upper portions of a left side plate and a right side plate, a screw sleeve is connected to the screw rod in a threaded mode, and the upper portion of the screw sleeve is slidably connected with a top plate; the upper clamping block is fixedly mounted at the bottom of the screw sleeve, the lower clamping block is fixedlymounted at the telescopic end of a first electric push rod, and the upper clamping block and the lower clamping block are of the same semicircular ring structure; and liquid storage cavities are formed inside the upper clamping block and the lower clamping block, a plurality of paint brushing rollers are rotatably mounted on the inner side of each of the upper clamping block and the lower clamping block, and a plurality of paint spraying heads are further rotatably mounted on the inner side of each of the upper clamping block and the lower clamping block. The upper clamping block of the semicircular ring structure and the lower clamping block of the semicircular ring structure are spliced into a complete circular ring, therefore, the paint spraying heads on the inner side of the circularring spray paint to the pipeline, and paint brushing is conducted through the paint brushing rollers, so that paint brushing is more uniform, the pipeline paint brushing efficiency is improved, and the labor intensity of workers is reduced.