Because main composition of by-product from flue gas desulphurization(BFGD)are CaSO_4, it can be used for improving sodic soils. A pot experiment was conducted to study the effect of BFGD on ameliorating sodic soil. There were eight treatments designed in this experiment, four BFGD levels(0,7.5, 15 and 22.5 t/hm~2)and two leaching levels(750 m~3/hm~2 and 80 m~3/hm~2). Results indicated that rate of sunflower emergence was increased, Exchangeable Sodium Percentage(ESP), pH, Total Dissolved Salts(TDS)and the ratio Na~ K~ /Ca~(2 ) Mg~(2 ) in water soluble salt were decreased by applying the by-product, but excessive BFGD also had effect on emergence and growth of sunflower, and leaching can improve the improvement efficiency. It's was inferred that the best BFGD requirement was 13.05 t/hm~2 when ESP =63.5, and pH =9. 15 according to the test result. The result of treatment 4 (7.5 t/hm~2 BFGD and 1200 m~3/hm~2 leaching water)was best in this experiment, the emergence rate and single output of sunflower are up to 92.5% and 36.40 g respectively.