In this study, chitosan was modified with quaternary ammonium salt. The optimal preparation conditions of chitosan quaternary ammonium salt were examined by single factor experiments. Its structure was characterized by Fourier infrared spectroscopy and hydrogen nuclear magnetic spectroscopy. The mechanical properties of the coating film prepared by chitosan quaternary ammonium salt with different degrees of substitution were investigated. Using chitosan quaternary ammonium salt as the raw material, with the introduction of polyvinyl alcohol, nano-titanium dioxide, and glycerol, chitosan quaternary ammonium salt-based composite membrane was prepared by the solution blending method. The structure and performance of the composite film of chitosan quaternary ammonium salt were examined by Fourier infrared spectroscopy, thermogravimetric analysis and contact angle measurements. The results revealed the optimal preparation conditions as follows: the mass ratio of quaternary ammonium salt to chitosan was 3:1, reaction time was 12 h, and reaction temperature was 80 ℃. In addition, when the content of chitosan quaternary ammonium salt was 50% (polyvinyl alcohol as the standard), nano-titanium dioxide content was 1%, and glycerol content was 0.8%, optimal tensile strength and elongation at break of chitosan quaternary ammonium salt-based composite membrane were achieved (19.38 MPa and 55.78%, respectively). The tensile strength of the chitosan quaternary ammonium salt-based composite membrane (19.38 MPa) was also higher than that of the chitosan composite membrane (18.64 MPa). This indicated that the modification of chitosan with quaternary ammonium salt was beneficial to the increase of the mechanical properties of the coating, which provides a certain theoretical reference for subsequent studies on membrane materials containing modified chitosan.