CO

2

is an important component in the acid gas and it is necessary to study the effect of CO

2

presence on the oxy-fuel combustion of H

2

S with particular focus on the formation of carbonyl sulfide (COS). The oxy-fuel combustion of acid gas was conducted in a coaxial jet double channel burner. The distribution of flame temperature and products under stoichiometric condition along axial (

R

= 0.0) and radial at about 3.0 mm (

R

= 0.75) were analyzed

respectively. The Chemkin-Pro software was used to analyze the rate of production (ROP) for gas products and the reaction pathway of acid gas combustion. Both experimental and simulation results showed that acid gas combustion experienced the H

2

S chemical decomposition

H

2

S oxidation and accompanied by H

2

oxidation. The CO

2

presence reduced the peak flame temperature and triggered the formation of COS in the flame area. COS formation at

R

= 0.0 was mainly through the reaction of CO

2

and CO with sulfur species

whereas at

R

= 0.75 it was through the reaction of CO with sulfur species. The ROP results indicated that H

2

was mainly from H

2

O

decomposition in the H

2

S oxidation stage

and COS was formed by the reaction of CO

2

with H

2

S. ROP and other detailed analysis further revealed the role of H

OH and SH radicals in each stage of H

2

S conversion. This study revealed the COS formation mechanisms with CO

2

presence in the oxy-fuel combustion of H

2

S and could offer important insights for pollutant control.