A composite metal foil and a preparation method thereof are provided. The composite metal foil includes a carrier layer, a barrier layer, a striping layer, and a metal foil layer. The carrier layer, the barrier layer, the striping layer, and the metal foil layer are sequentially stacked, the barrier layer includes a metal bonding layer and a high-temperature resistant layer stacked, and the metal bonding layer is disposed between the carrier layer and the high-temperature resistant layer. The striping layer is disposed between the carrier layer and the metal foil layer so as to facilitate peeling of the carrier layer, and the barrier layer is disposed between the carrier layer and the metal foil layer so as to prevent the carrier layer and the metal foil layer from diffusing mutually to cause bonding at a high temperature, so that the carrier layer and the metal foil layer are easy to peel off. In addition, the metal bonding layer is disposed between the carrier layer and the high-temperature resistant layer, so that the barrier layer is not easy to separate from the carrier layer, and peeling between the barrier layer and the carrier layer is prevented.