Abstract: Large-sized polyimide (PI) nanofiber aerogels with 0.3%–0.7% mass fraction of PI nano-fiber were prepared by optimized template freeze-drying method at different freezing temperatures (−50, −20, 0 ℃). The microstructure, thermal conductivity, mechanical properties, dielectric properties and sound absorption property of the aerogels were investigated. The results show that the maximum size of PI nano-fiber aerogels prepared by template freeze-drying method could reach 50 cm×50 cm×1 cm. The pores of PI nano-fiber aerogels prepared at −20 ℃ were smaller and the fiber distribution was more uniform. With 0.3%–0.5% mass fractions PI nano-fiber, the density of the aerogels was (3–5)×10⁻³ g·cm⁻³, and the thermal conductivity was in the range of 0.023 6–0.026 6 W·m⁻¹·K⁻¹, the maximum compressive strain was greater than 90%, and the elastic modulus was in the range of 1–3 kPa. The dielectric constant at 1 MHz of 0.3% mass fraction of PI nano-fiber was 2.65, which was less than PI solid resin, and the average acoustic absorption coefficient at 4 000–6 400 Hz of 0.4% and 0.5% mass fractions of PI nano-fiber was 0.86. The PI nanofiber aerogels had the advantages of ultra-light weight, low thermal conductivity, good flexibility and resilience.