The invention relates to an energy-conservation separation method and an energy-conservation separation device for rectifying dimethyl ether. The device comprises a gas-liquid separation tank, a gas distributor, a gas-liquid mixer, a raw material condenser, a rectifying tower, a reboiler, a condenser and a machine pump, wherein the condenser is arranged at the tower top of the rectifying tower; and the reboiler is arranged at the tower bottom of the rectifying tower. The method comprises the following steps: performing flash evaporation on a high-temperature mixture by using the gas-liquid separation tank, thereby dividing into a gas-phase mixture and a liquid-phase mixture; and distributing the gas-phase mixture into two strands by using the gas distributor, wherein one strand of the gas-phase material serves as a condensate liquid-phase feeding material which enters the middle upper parts of the rectifying section of the rectifying tower after being condensed into the liquid-phase material by using the raw material condenser, so that the temperature of the rectifying section can be lowered and the load of the condenser at the tower top can be reduced; and the other strand of the gas-phase material is used as a mixed-feeding gas-phase material which enters the middle lower part of the rectifying section of the rectifying tower after being mixed with the liquid-phase mixture from the gas-liquid separation tank, so that the partial energy can be provided for the tower kettle reboiler. According to the method and the device, the energy consumption during production is lowered obviously; and the operation load of the rectifying tower is also decreased obviously; so that the residual quantity of the dimethyl ether at the tower bottom of the rectifying tower is lowered to a minimum extent. As a result, the purposes of energy conservation and emission reduction are achieved.