Sulphur hexafluoride (SF6) has been specified as a greenhouse gas. The root causes of the great insulating performance of SF6 such as microscopic structure are still worth studying to find other alternative insulating gases. Many researches of trifluoroiodomethane (CF3I) have shown that CF3I has many excellent properties which make it one of the possible alternatives of SF6. In this paper we attempted to explore part of the microscopic reasons for their insulating properties. We started research from atomic and molecular physics features such as atom compositions, molecular structures and covalent bonds of some organic insulating gases to expound the significant relationships between molecular properties and electron attachment processes. For the same list of molecular features we compared SF6 and CF3I to get the necessary microscopic features as basic condition which can be used in the pre-analysis of insulating performance for new gases. Additionally, it can also be used to research gas mixtures for insulating characteristics complements from the point of view of microscopic properties.