A flue gas treatment method at least removes sulfur dioxide and dust particles in flue gas through gas-liquid contact with absorption fluid, which comprises: applying a gas-liquid contact device with a tank, and inputting the absorption fluid into the tank; An inlet-side absorption tower extending upward from a lateral position of the tank and having an equal cross-sectional shape, wherein the absorption fluid in the tank is injected upward from a plurality of horizontally spaced positions in the form of liquid columns, so that untreated flue gas is in gas-liquid contact with the absorption fluid; And an outlet-side absorption tower extending upward from the other side of the tank and having the same cross-sectional shape, wherein the absorption fluid in the tank is injected upward from a plurality of horizontally spaced positions in the form of liquid columns, so that the flue gas leaving the inlet-side absorption tower and the absorption fluid are in gas-liquid contact again; One of the inlet side absorption tower and the outlet side absorption tower is made into a cocurrent absorption tower, and the flue gas in the tower flows downwards; Setting the flue gas velocity in the cocurrent absorption tower at a high value is beneficial to dust collection and sulfur dioxide absorption; At the same time, other structures of the inlet side absorption tower and the outlet side absorption tower are made into countercurrent absorption towers, and the flue gas in the countercurrent absorption tower flows upward, and the flue gas flow rate in the countercurrent absorption tower is set at a low value, which is beneficial to the countercurrent gas-liquid contact absorption of sulfur dioxide; And controlling the flow rate of the absorption fluid flowing to the parallel flow absorption tower, so that the concentration of dust particles in the treated flue gas will have an expected value; The flow rate of absorption fluid flowing to another counter-current absorption tower is controlled so that at least the concentration of sulfur dioxide in the flue gas to be treated will have a desired value.