In this study, a fluid model has been used to study the effect of gas mixing ratio and pressure on the density distribution of important etchant species, i.e., hydrogen (H), bromine (Br), Br + , and HBr + in HBr/He plasma. Our simulation results show that the densities of active etchant species H, Br, and HBr + increase with the increase in pressure as well as the HBr fraction in HBr/He mixture. On the contrary, the density of Br + decreases with the increase in He percentage in HBr/He mixture and with the increase in the pressure. Time averaged reaction rates (of the reactions involved in the production and consumption of these species) have been calculated to study the effect of these reactions on the density distribution of these species. The spatial distribution of these species is explained with the help of the time averaged reaction rates. Important reactions have been identified that contribute considerably to the production and consumption of these active species. The code has been optimized by identifying 26 reactions (out of 40 reactions which contribute in the production and consumption of these species) that have insignificant effect on the densities of H, Br, Br + , and HBr + . This shows that out of 40 reactions, only 14 reactions can be used to calculate the density and distribution of the important species in HBr/He plasma discharge.