The invention discloses a method for preparing a quaternary ammonium salt chitosan and polyvinyl alcohol antibacterial filter composite material. The method is characterized by comprising the following steps: mixing and stirring chitosan powder, acetic acid and deionized water to form a chitosan acetic acid solution; adding isopropyl alcohol, stirring and standing; heating a container through a water bath, and dropwise adding a certain amount of 2,3-epoxypropyltrimethylammonium chloride at set intervals to react; at the end of the reaction, adding absolute ethanol to the container, precipitating, performing suction filtration, and then soaking with acetone, washing, performing suction filtration, and drying to obtain modified quaternary ammonium salt chitosan; preparing a spinning solutionfrom the modified quaternary ammonium salt chitosan, and adding the spinning solution into a polyvinyl alcohol spinning solution to be mixed and stirred to obtain a mixed spinning solution, and obtaining the composite material by an electro-spinning method. The method disclosed by the invention satisfies the development requirements that the material is light and thin, and has good filterabilityand excellent antibacterial performance and the like in practical application, and can be used for preparing biomedical antibacterial protective materials such as biofiltration membranes, protective masks, wound dressings and the like.