The effect of high-pressure carbon dioxide on ionic conductivity for comb-like type polyether electrolytes based on oligo(oxyethylene glycol) methacrylate with lithium triflate, LiCF3SO3, has been investigated for the first time. Our investigations have focused on the correlation between the segmental motion of the polymer side chains and the efficiency of ion transport under supercritical carbon dioxide (scCO2) conditions. Consequently, the ionic conductivity under the condition of 10 MPa and 40°C CO2 sample was more than 30 times elevated compared with the original one. The improvement of ionic conductivity is attributed to an increase in the polymer segmental motion via a decrease in activation volume and enhanced the number of charge carriers. The temperature dependence of log σ followed Vogel–Tamman–Fulcher (VTF) equation. However, the pressure dependence under scCO2 condition was ascribed to the Arrhenius behavior resulting in an increase of the ionic conductivity with increasing the pressure.