The invention discloses a composite coating device. The composite coating device comprises a base, a sliding rail located on the base, and slides mounted on the sliding rail. A motor is mounted on thebase. A first side plate and a second side plate are fixedly connected with the left side and the right side of the base correspondingly. The slides are vertically connected to the sliding rail through slide bases. Two-directional threaded rods are rotationally arranged on the two slides. Two coating assemblies are in threaded connection with each two-directional threaded rod. Connecting rods arerotationally arranged on the slide bases. First helical teeth are connected with the ends, located in the slide bases, of the connecting rods. A cambered surface of each coating assembly is divided into a first area, a second area, a third area and a fourth area. One of the areas of each coating assembly is provided with an outlet and an inlet. The four coating assemblies are sequentially distributed on the circumference in the mode that the first area of the first coating assembly is provided with the outlet and the inlet, the second area of the second coating assembly is provided with the outlet and the inlet, the third area of the third coating assembly is provided with the outlet and the inlet, and the fourth area of the fourth coating assembly is provided with the outlet and the inlet. According to the composite coating device, different coating technical steps can be conducted by the four coating assemblies, and the composite coating device is suitable for coating of pipelines with different pipe diameters.