Polyaniline-coated multi-walled carbon nanotube conductive polymer precursors (MWCNTs@PANI) were prepared by an in situ microemulsion oxidation polymerization of aniline in the case of multi-walled carbon nanotubes (MWCNTs), and then hydroxyl-terminated polybutadiene polyurethane conductive polymer nanocomposites based on MWCNTs@PANI (MWCNTs@PANI/HTPB PUs) were prepared through an in situ stepwise polymerization of HTPB and diisocyanates. The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR), Raman, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The morphologies and dispersion behavior were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis transmittance. The MWCNTs@PANI/HTPB PUs nanocomposites were fabricated into film sensors for detection of volatile organic compound (VOC) vapors, and displayed an evident response to trichloromethane vapor (CHCl3). The effect of MWCNTs on the conductivity and the responsivity of conductive polymer nanocomposite films to trichloromethane were studied, finding that the conductive composite films have fast and strong response, good repeatability and recoverability, and long-term stability. Consequently, they can be potentially applied for supervision and detection of interior and outdoor environmental gases or vapors.