Double nanofillers are becoming an important and effective strategy to reinforce and functionalize polymeric materials, and maximizing the strength of nanofillers to compensate for their weaknesses remains of great interest in the field of nanocomposite. Herein, we report a facile and efficient double-nanofiller strategy to reinforce polyimide fibers. After grafting 3-aminopropyltriethoxysilane (APTES) onto fluorinated multiwalled carbon nanotubes (F-MWCNTs), the functionalized MWCNTs, APTES@F-MWCNTs, reacted with silica sol via the reactions of Si-OH groups. Because of the formation of chemical bonds, dispersibility of MWCNTs was improved by the assistance of a grafted silica sol; MWCNTs prevent the silica sol from diffusing into a coagulation bath and being lost of silica during wet-spinning. Synergistic "anchor" effect of carbon nanotubes and silica results in a considerable improvement of mechanical properties (44.4%) of polyimide fibers and an increase in the T-g value from 348 to 381 degrees C.