A process of simultaneous desulfurization and denitrification of flue gas was conducted in this study. The flue gas containing 200 mg·m

-3

NO

1000-4000 mg·m

-3

SO

2

3%-9% O

2

and 10%-20% CO

2

was first oxidized by O

3

and then absorbed by ammonia in a bubbling reactor. Increasing the ammonia concentration or the SO

2

content in flue gas can promote the absorption of NO

X

and extend the effective absorption time. On the contrary

both increasing the absorbent temperature or the O

2

content shorten the effective absorption time of NO

X

. The change of solution pH had substantial influence on NO

X

absorption. In the presence of CO

2

the NO

X

removal efficiency reached 89.2% when the absorbent temperature was raised to 60 °C

and the effective absorption time can be maintained for 8 h

which attribute to the buffering effect in the absorbent. Besides

both the addition of Na

2

S

2

O

3

and urea can promote the NO

X

removal efficiency when the absorbent tempe

rature is 25 °C

and the addition of Na

2

S

2

O

3

had achieved better results. The advantage of adding Na

2

S

2

O

3

became less evident at higher absorbent temperature and coexistence of CO

2

. In all experiments

SO

2

removal efficiency was always above 99%

and it was basically not affected by the above factors.