The invention discloses a forming device and method of a complex inner wall and outer wall cylindrical part. The forming device comprises a concave die separation mechanism, an inner and outer sectiondie separation mechanism and a cylindrical convex die mechanism. The concave die separation mechanism is composed of a multi-section concave die and concave die drive cylinders. The multi-section concave die is of a two-section or four-section vertical symmetric structure, a hydraulic cylinder is used for controlling so that automatic die combining and separation can be achieved, a die cavity inthe shape of the outer wall of the part is arranged in the multi-section concave die. The inner and outer section die separation mechanism is mainly composed of the hydraulic cylinder, inner and outercore shafts and inner and outer section dies, the outer edges of the inner and outer section dies coincide after die separation, and a mold chamber in the shape of the inner wall of the part is formed. The cylindrical convex die moves vertically through the drive cylinder to achieve one-time forming of the cylindrical part in the complex shape. According to the forming device and method, the problems existing to the manufacturing processes of traditional extrusion forming, casting, welding and the like when the part in the complex shape is formed are effectively solved, material consumption is low, cost is saved, and the forming device and method are suitable for large-batch production.