As one of polymer nanocomposite, carbon nanotube(CNT)/polymers is expected to be stable and high strength and conductive materials than other polymer composites. However, high aspect ratio CNTs, which is necessary for the high performance, tend to break and buckle and become lower aspect ratio CNTs when they are mixed with polymers and the developed materials shows some little increased properties compare to that as be expected. In this study, we have applied the high-pressure fluid mixing method (HPFM) for developing the CNT/polymer nanocomposite. It is because HPFM is a mild and effective mixing method for less breaking the CNT in mixing process under supercritical CO2 (SCCO2) atmosphere and also has benefit to disperse the chemical substances such as chemical cross linkers, dissolved in SCCO2 into the composited polymers in nanoscale. As a model study, we have carried out the mixing with fluorine-based polymer, cross-linker, and cross-linked aided additive by the HPFM under the lower temperature than the cross-linked temperature and then the samples were cross-linked by the hot-press under the higher cross-linking temperature. We investigated the change of the properties by tensile test and found that in spite of an amount of cross-linkers are extracted by SCCO2 in the mixing, the mechanical properties of tensile stress developed samples were better than that of developed by the conventional mixing. It will mean that cross-linkers and its enhancer distributed in uniformly in high modulus polymer nanocomposites by the HPFM. Polymer melts mixing under SCCO2 atmosphere will be an effective mixing modification for developing a nanocomposite and reactive blending.