Light but robust porous ceramic fibers with combined properties of super flexibility, excellent thermal stability and thermal insulation performance are attractive for use in extreme conditions, especially in the field of aerospace. However, the practical application of traditional porous ceramic fibers are usually limited by their brittle nature and poor mechanical properties. Herein, we designed a multichannel SiZrOC ultrafine fiber (MSUF) composed of ZrO2, SiOxCy and free carbon phases by electrospinning technique. The resulting fibers exhibited integrated properties of excellent fire resistance, high temperature stability, thermal shock resistance and temperature-invariant flexibility. More importantly, the fancy multichannel structure and components of the fiber provides it with outstanding thermal insulation performance with low thermal conductivity (0.041 W m-1·K-1 at 25 ºC and 0.141 W m-1·K-1 at 1000 ºC). The successful fabrication of such flexible porous MSUFs may provide a new approach to design high performance thermal insulators for high temperature thermal insulation.