Carboxyl modified carbon nanotubes (H‐CNTs) are added into 10 wt%‐polyamide 66/90 wt%‐polyphenylene (10‐PA 66/90‐PPS) blending system to improve the compatibility of blends. In order to investigate the effects of H‐CNTs selective location and H‐CNTs addition on the structures, morphologies, and properties of PPS/PA 66 composite fibers, three blending orders among H‐CNTs, PPS, and PA 66 are applied in the blending extrusion of ternary resins. The structures, morphologies, and properties of composite fibers are characterized via scanning electron microscopy, transmission electron microscopy, high‐pressure capillary rheometer, differential scanning calorimeter, tensile test, and dry heat shrinkage test. Experimental results indicate that the migration of H‐CNTs from PPS phase to the interface between PPS and PA 66 results in the increases of the crystallinity of PPS, the tensile strength and the high‐temperature resistance of ternary fibers. When H‐CNTs are blended with PA 66 firstly, the locking effects of H‐CNTs causes a phase‐inversion phenomenon, where major component PPS forms dispersed phase and minor component PA 66 forms continuous phase. Even though this phenomenon weakens the mechanical properties and the high‐temperature resistance of composite fibers, the shrinkage of composite fibers at high temperature is improved.