The invention discloses a device for preparing an egg-type composite alloy welded ball and a preparation method thereof. The traditional uniform drop jetting device is utilized, a cylindrical internal screw liquid nitrogen circulating cooling device is added, a spiral pipe is filled with flowing liquid nitrogen, and the temperature in the cooling device can be maintained to be within an appropriate range. When a high temperature drop-state alloy metal welded ball enters into a spiral-type cooling device, and heat transfer is carried out between exterior of the drop-state alloy metal welded ball and air in a cavity, thus a temperature gradient is formed between the inner core and the shell of the welded ball, and the temperature gradient causes the welded ball to form a layered egg-type structure. By utilizing the technical scheme in the invention, the drop-state alloy metal welded ball can form a layered structure that the center is a Cu core and the exterior is Sn-Bi alloy in a falling process, thus a core-shell structure can be rapidly formed and the welded ball with better comprehensive properties can be obtained.