Polyimide (PI) aerogels were successfully synthesized via a straightforward sol-gel process under room temperature along with the supercritical CO2 drying method using 4-amino- N-methylbenzamide and 3,3',4,4'-biphenyltetracarboxylic dianhydride. 1,3,5-Triaminophenoxybenzene was used as the cross-linker. The chemical structure, pore structure, morphology, thermal performance, CO2 adsorption, and mechanical performance of PI aerogels were investigated. The as-prepared PI aerogels had low bulk densities (0.091-0.167 g/cm3), low shrinkages (9.73-17.36%), low thermal conductivities (0.0307-0.0341 W/m·K), high specific surface areas (449.76-538.19 m2/g), small pore diameter (10.37-22.41 nm), high thermal stability (onset of decomposition above 560 °C), and excellent mechanical property. The CO2 adsorption capacities of PI aerogels were substantially higher than the values of the previous porous materials reported under the similar conditions, and the CO2 uptake capacity was as high as 31.19 cm3/g at 25 °C and 1.0 bar. The resulting PI aerogels could be potentially used as thermal insulators and CO2 adsorbents.