The invention discloses an electricity-water combined supply device and a method for seawater desalination by using flue gas waste heat of a micro gas turbine. The device comprises a micro gas turbine, a distiller and a heat exchanger, wherein a smoke supply pipeline and a start bypass are arranged at a high-temperature flue gas outlet of the micro gas turbine; the smoke supply pipeline is connected with the heat exchanger; the heat exchanger is connected with a smoke discharge pipe; a heat-transfer medium outlet of the distiller is connected with a heat-transfer medium inlet of the heat exchanger through a pipeline; a heat-transfer medium outlet of the heat exchanger is sequentially connected with an electric auxiliary hot water tank and a heat-transfer medium inlet of the distiller through pipelines; the distiller is connected with a product water tank through a pipeline; a strong brine discharge port and an original seawater inlet are formed in the distiller; an original seawater inlet pipe is connected with the original seawater inlet. The device disclosed by the invention uses the high-temperature flue gas discharged by the micro gas turbine as a heating heat source, and the heat-transfer medium is heated at first and then enters the distiller to heat the original seawater so as to produce fresh water, so that electricity-water combined supply is realized, the gradient utilization of energy in a system is realized, and the comprehensive utilization of fuels is improved.