A high-power resistor and a fabrication method thereof are provided. The method includes: providing a resistance substrate including resistance alloy material and a copper metal layer; forming a cuprous oxide layer on the resistance substrate by using the copper metal layer; sticking the resistance substrate to a ceramic substrate, in which the cuprous oxide layer is located between the resistance substrate and the ceramic substrate; performing a sintering process on the resistance substrate and the ceramic substrate to form a composite substrate; forming a plurality of terminal electrodes on the composite substrate to form the high-power resistor. Therefore, the high-power resistor includes the composite substrate and the terminal electrodes. The composite substrate includes a bonding layer disposed between the ceramic substrate and the resistance substrate to bond the resistance alloy material on the ceramic substrate, in which the bonding layer includes sintered cuprous oxide.