The invention discloses a device for separating oil from water through afterheat. The device comprises a housing, a heat dissipating port, a water storing tank, an oil-water tank and a steam absorbingpipe, wherein the heat dissipating port is formed in the top part of the housing; the water storing tank is arranged at the upper part of the heat dissipating port and is fixed to the ground througha plurality of supporting rods; a plurality of water inlet pipes are arranged on the water storing tank, and the oil-water tank is arranged in the water storing tank; and the steam absorbing pipe is arranged at the upper part of the oil-water tank. Compared with the prior art, the device has the advantages that the structure is reasonable; the afterheat in the housing is dissipated through the heat dissipating port; water is poured into the water storing tank, and oil water is poured into the oil-water tank; water is boiled and evaporated under a water bath heating condition; the steam is cooled into water through the steam absorbing pipe, and then the water is collected in a water collecting barrel, and oil is in the oil-water tank, so that the oil and water separation is realized; and meanwhile, the afterheat produced in the housing can be reasonably utilized; the utilization rate of the oil and the water is increased; and the waste of heat energy is reduced.