Abstract: The removal efficiency of NO has become the bottleneck of the development of double towers system for simultaneous biological removal of SO2 and NOx ． In order to increase the microbial removal rates of NO and NOx from the flue gas，a solution of FeSO4·7H2O was added into the desulfurizing tower， and a certain concentration solution of NaNO2 was added into the denitrification tower，which were investigated on the effects on double towers system． The results demonstrated that the mean removal rates ( Abbrev． rates) of NO was 61. 04% when the dosage of FeSO4·7H2O was 0. 23 g /L， increasing by 25. 73% compared with blank test; the removal rates of NOx was 62. 16% in desulfurizing tower，which increased 31. 06% than the blank test; and the capacity of purifying NOx of double towers system improved from 61. 8% to 86. 9%． The concentration gradient experiment results showed that the suitable concentration of FeSO4·7H2O was 0. 23 g /L． Besides， the removal rate of NO by denitrification tower increased from 39. 92% to 52. 11% with the dosage of NaNO2 being 0. 5 g /L; and the NOx removal rate increased from 47. 67% to 58. 90%． Meanwhile，the removal rate of NOx in the double towers system was 79. 32%，while the blank test was 70. 75%． Verification tests for many times proved that adding FeSO4 and NaNO2 could enhance the microbial purification efficiency of NO and NOx in simulated flue gas．