The invention discloses an oil-water separation and automatic liquid discharge device for a gas-liquid separator, which is applied to the technical field of oil-water separation in natural gas production of oil and gas fields. The automatic liquid discharge device disclosed by the invention is characterized in that an oil-water clapboard is welded in a lower cylinder, and the upper end of the external wall of the lower cylinder is provided with a flange; an oil-water clapboard is welded in an upper cylinder, and a distance is formed between the upper end of the oil-water clapboard in the upper cylinder and the top of the upper cylinder; the lower end of the external wall of the upper cylinder is provided with a flange; the upper cylinder is connected with the flange of the lower cylinder,and the interior of the upper cavity and the interior of the lower cavity are respectively formed into a water cavity and an oil cavity, and the top of the water cavity and the top of the oil cavity are communicated; a water outlet and an oil outlet are fixed on the wall of the lower cylinder, and the inner end of the water outlet and the inner end of the oil outlet are respectively connected with a valve; the interior of the water cavity is provided with a water drainage buoy, the interior of the oil cavity is provided with an oil drainage buoy, the lower end of the water drainage buoy and the lower end of the oil drainage buoy are respectively connected with a buoy lever, and the other ends of buoy levers are connected with the valve plugs of the valves; and an oil-water mixed liquor inlet is fixed on the wall of the upper cavity. The oil-water separating automatic liquid discharge device disclosed by the invention has the effects of realizing the automatic separation and automatic liquid discharge of oil and water, and realizing the unattended management, thereby reducing the staff labor.