A multi-mode microwave heating device includes a heating chamber, a plurality of microwave transmitters, a plurality of longitudinal-polarized rectangular waveguides, a plurality of transverse-polarized rectangular waveguides, and a plurality of half-wave-rectified power supplies. The heating chamber has a holder for holding a to-be-heated object. The holder is connected to a rotating and an elevating mechanism. The microwave transmitters are connected to the heating chamber through the longitudinal-polarized rectangular waveguides as well as connected to the transverse-polarized rectangular waveguides for transmitting microwaves into the heating chamber and to excite multiple cavity modes of the heating chamber, so as to achieve uniform microwave heating. An industrial three-phase alternating current (AC) power source offers multi-phased electricity to the half-wave-rectified power supplies, by which the microwave transmitters are powered, such that the multiple modes are decoupled and uniform microwave heating are achieved.