The invention discloses a preparation method of a copper-aluminum composite wire, which belongs to the field of composite material processing and heat treatment. A copper tube blank is prepared by deep hole processing; an aluminum bar blank is prepared by hot extruding, and the aluminum bar blank is machined to make the outer diameter of the aluminum bar blank smaller than the inner diameter of the copper tube blank; the aluminum bar blank is arranged in a sleeved manner in the copper tube blank, composite rolling is carried out by three-roll planetary rolling, and then, multi-pass drawing andheat treatment are carried out to obtain a copper-aluminum composite wire. The copper-aluminum composite wire prepared by the method avoids the formation of inter-metallic compounds in the preparation process, has large deformation during rolling, and has good interface bonding performance.