Disclosed is a device for painting the inner wall of an oval pipeline. A motor drives a central rotary shaft to rotate, the central rotary shaft transmits power to rotary wheels, the rotary wheels drive painting assemblies installed on the rotary wheels to rotate, and the movement track of painting heads of the painting assemblies is an oval similar to the inner wall of the oval pipeline to becleaned. While the central rotary shaft rotates, an air blower presses paint in paint painting cavities in T-shaped rods of the painting assembliesinto paint jetting openings through pressure hoses, then the paint enters jetting holes of the painting heads, and brushes on the painting heads paint the inner wall of the oval pipeline while rotating. The inner wall of the oval pipeline is efficiently painted;labor intensity of painting of the inner wall of the oval pipeline is relieved; andthe paint and the like are prevented from adhering to the body and clothes of an operator, and injuries of toxic substances in the paint to the body of the operator during long-termmanual painting are avoided. For the oval pipeline of which the diameter is too small to allow the operator to enter, the inner wall of the oval pipeline can be painted by the device, the dead angles of painting are avoided, and the painting effect is good.