The invention relates to the field of coal burning flue gas pollutant purification, and discloses a flue gas purification system and method. The flue gas purification system comprises an absorption tower and a stock tank outside the absorption tower. An in-tower stock tank, a primary spraying layer, and a secondary spraying layer are sequentially arranged in the absorption tower from bottom to top. The flue gas purification system also comprises a primary supply device for delivering slurry in the in-tower stock tank to the primary spraying layer and a secondary supply device for delivering slurry in the stock tank outside the absorption tower to the secondary spraying layer; and the pH of the slurry in the stock tank outside the absorption tower is greater than the pH of the slurry in thein-tower stock tank. Through the technical scheme mentioned above, the primary spraying layer sprays slurry with a lower pH value, the secondary spraying layer sprays slurry with a higher pH value, the mass transfer effect is enhanced; SO2 is absorbed in different areas and levels, and finally the discharge standard that SO2 content of flue gas is not higher than 10 mg/Nm3 is reached. The provided flue gas purification system can improve the desulfurization efficiency and reduces the energy consumption and cost at the same time.