Abstract: He+Air plasma is a common type of cold atmospheric plasma with typical characteristics of numerous reactive species and complex reactions, making it difficult to conduct experiments systematically, and hence, numerical study becomes important. However, few of existing models have considered CO₂ in the air even though our group and co-workers have found that trace gas content may have great influences on the production of reactive species in plasma. In the view of this, we took CO₂ and its 7 kinds of discharge products and 120 relating chemical reactions into account on the basis of our He+Air plasma global model reported previously, and investigated the reaction kinetics of the plasma under the conditions of 5 typical concentrations of CO₂ in ground air. Results show that the reaction conversion of CO₂ is more than 37% when the input power density is 10 W/cm³, in which the ionization process is enhanced while the dissociation and attachment process is weakened in the plasma. The average density of reactive species in He+Air plasma can be changed by 1.8%~11.2% when CO₂ is considered with concentrations in the common range in ground air. In this paper, the significant influence of trace CO₂ on the reactive species in He+Air plasma is quantified, and it is found that the variance of CO₂ concentration in different areas will obviously change the chemical reactivity of a specific plasma source, which can be used as a reference for biomedical applications.