The invention discloses a gas-liquid separator and a gas-liquid separation method. The gas-liquid separator is provided with a columnar cyclone separator; the columnar cyclone separator comprises a vertical tube body (9); a partition plate (402) is arranged in the vertical tube body; an air lifting pipe (401) is arranged in the middle of the partition board; a circle of downcomer tubes (403) are arranged downwards, and are close to the edge of the partition board; the gas-liquid separator is also provided with a tubular preseparator; the tubular preseparator is provided with a gas phase tube (105) and a liquid phase tube (106); the gas phase tube and the liquid phase tube are both connected with the vertical tube body along the tangential direction of the vertical tube body; the outlet ofthe gas phase tube is located above the top outlet of the gas-raising tube; the outlet of the liquid phase tube is located below the bottom outlets of the downcomer tubes; and a liquid drop sedimentation region (2) and a bubble floating region (5) are arranged in the vertical tube body. The invention discloses the gas-liquid separation method by adopting the gas-liquid separator. The gas-liquid separator provided by the invention is mainly used for gas-liquid separation in the technical field of oil-gas treatment in oil and gas fields.