Reactions of active nitrogen with SO 2 and SOCl 2 have been studied on a flowing afterglow apparatus. The emissions ranging from 280 to 500 nm were assigned to SO 2 ( A ˜ 1 A 2 , B ˜ 1 B 1 → X ˜ 1 A 1 ) and SO 2 ( a ~ 3 B 1 → X ˜ 1 A 1 ) With the aim of discerning the roles of active N atom and N 2 ( A 3 Σ u + ) played in the reactions above, N 2 ( A 3 Σ u + ) generated by Ar( 3 P 0,2) reacting with N 2 has substituted the active nitrogen to react with SO 2 and SOCl 2, respectively. It shows that when reacting with SO 2, both active nitrogen and N 2 ( A 3 Σ u + ) without N atom can produce SO 2 ( A ˜ 1 A 2 , B ˜ 1 B 1 ) and SO 2 ( a ˜ 3 B 1 ) . While reacting with SOCl 2, only when N 2 ( A 3 Σ u + ) and the active N atom coexist could SO 2 ( a ˜ 3 B 1 ) be formed. Therefore, it is concluded that N 2 ( A 3 Σ u + ) dominates the reaction of active nitrogen with SO 2 and excites SO 2 directly; N 2 ( A 3 Σ u + ) and active N atom reacting with SOCl 2 can generate the constitutions to form SO 2 ( a ˜ 3 B 1 ) , which were suggested as N 2 O ( X 1 Σ + ) and SO( X).