The invention discloses a cylindrical expansion tank for air source heat pump heating and a manufacturing method thereof. Slide rails are arranged on the inner wall of a barrel body in the expansion tank, a side pressing steel plate is arranged on each slide rail, and a U-shaped supporting part is arranged between the two side pressing steel plates. A sliding device is arranged on the outer side of each side pressing steel plate, a U-shaped mounting seat is arranged between the two side pressing steel plates, and an air bag is arranged in the U-shaped mounting seat. The manufacturing method includes the steps of (a) manufacturing of an upper end cover, (b) manufacturing of a lower end cover, (c) stretching forming of the barrel body, (d) welding and fixing of the upper end cover and the barrel body, (e) cleaning of the upper end cover and the barrel body, (f) fixing of the side pressing steel plates and the U-shaped supporting part, (g) sliding of the air bag, (h) fixing of the air bag, (i) welding and fixing of the lower end cover and the barrel body, (j) pre-inflation at an inflating opening of the air bag, and (k) labeling and packaging. The mounting portion of the air bag and the mounting portion of the upper end cover are precisely aligned, so that mounting difficulty is lowered; and lateral supporting on the air bag is achieved, and the air bag shock absorption effect is achieved.