Although SF6 gas has good insulation performance, due to its strong greenhouse effect, the search for alternative gas of SF6 has become a research hotspot of scholars at home and abroad. In this paper, the discharge parameters of SF6/CO2/N2 and CF3I/CO2/N2 mixed gases with different ratios are calculated by Boltzmann equation analysis method, and their critical critical breakdown field strength is obtained. The experimental study is 0.1MPa. Power frequency breakdown characteristics of SF6/CO2/N2 and CF3I/CO2/N2 mixed gas under uniform electric field. It found through experiments that the critical breakdown field strength obtained by the Boltzmann equation analytical method and the critical breakdown field strength obtained by the power frequency breakdown voltage are numerically different, and the mixed gas insulation of different ratios is different. A preliminary prediction of the strength made to select a mixed gas with better insulation performance and greater substitution possibilities for further research.