The invention discloses a combined forming device for a motor shaft. The device comprises a left die holder, a right die holder, a first combined concave die, a second combined concave die, a third combined concave die, a limited unloading device, and an unloading device, wherein the left die holder is opposite to the right die holder; the first combined concave die is arranged at the inner side of the left die holder by means of a left concave die fixing plate; the second combined concave die and the third combined concave die are arranged in sequence at the inner side of the right die holder by means of right concave die fixing plates; the limited unloading device is arranged at the inner side of the left die holder and located at the outer side of the left concave die fixing plate; the unloading device is arranged in the middle of the outer side of the right die holder. The invention also discloses a combined forming method for a motor shaft, wherein a pressure slider slides to draw the left and right die holders close to each other, and meanwhile, extrusion forming is carried out on a blank by means of the combined concave dies on the left and right die holders; after forming, quick unloading is achieved by means of the limited unloading device and the unloading device. One-step cold-extrusion forming of a motor shaft is achieved, and the production efficiency of the motor shaft is improved; the product quality is guaranteed, and the cost is low; the device is simple.