Mechanical properties of polyurethane coating were improved by multi-walled carbon nanotubes (MWNTs) via in situ polymerization and blending polymerization. Fourier transform infrared spectroscopy (FT-IR) measurement was employed to assess the influence of acid treatment on MWNTs. Mechanical properties analysis of polyurethane coatings including tensile strength, elastic modulus, hardness, flexibility, impact resistance were employed to assess the improvement of mechanical properties of polyurethane coating by MWNTs. The results indicated that MWNTs could improve the mechanical properties of polyurethane coatings, and the improvement of polyurethane coatings by MWNTs via in situ polymerization were better than via blending polymerization, and the improvement of polyurethane coatings by acid-treated MWNTs were better than by raw MWNTs.