The present disclosure provides a composite substrate for an antenna module, which includes: a first non-magnetic substrate that is configured to have a first copper foil; a second non-magnetic substrate that is configured to have a second copper foil; and a magnetic sheet that is configured to be interposed between the first non-magnetic substrate and the second non-magnetic substrate and that is configured to be integrally laminated with the non-magnetic substrates, and further provides a preparation method thereof. The present disclosure provides a simplification of a process, low costs, a slim design, and a grip-feeling of a metal material while providing functions of wireless charging, MST, and NFC.