The invention discloses an oil-water separation method and an oil-water separation device. The device consists of a primary oil-water separation unit, an adsorption and desorption unit, an advanced oil-water separation unit and a drainage unit, wherein a breather pipe is arranged at the top end of the primary oil-water separation unit and communicated with the atmosphere, and a transverse communicating hole is formed in the upper part of a partition between the adjacent units; a coarse grid residue basket in the primary oil-water separation unit is communicated with a fine grid residue basket by virtue of a diversion opening, and both the coarse grid residue basket and the fine grid residue basket are turnover and removable; an oil discharge mechanism consisting of a floating ball accommodating cavity, a floating ball and a plugging cylinder is connected with an oil discharge pipe; an adsorption and desorption packing layer is arranged in the adsorption and desorption unit; the advanced oil-water separation unit is provided with the oil discharge mechanism; the drainage unit is provided with a drainage pipe. The method and the device can be used for continuous, automatic and efficient oil-water separation without manual operation and energy consumption, and can be used for clearing sludge without power equipment, so that the energy is effectively saved; water can be prevented from entering the oil discharge pipe at a peak drainage period, so that the oil-water separation is more thorough.