The invention provides a chitosan filtering membrane. The chitosan filtering membrane can be used for filtering water by means of uniformly fixing chitosan on the surfaces or the internal parts of filtering base layers due to a characteristic of strong absorption capability of the chitosans. The used filtering base layer is made of cloth, plastic, paper or a metal net. The chitosan can be clamped between the two filtering base layers or mounted in a bag formed by the filtering base layers; and the chitosan contained in the bag is particle-shaped or powder-shaped. The chitosan filtering membrane provided by the invention can be used for effectively filtering harmful matters, such as bacterium, microorganism and heavy metal. Tap water, well water and underground water filtered by the chitosan filtering membrane provided by the invention can be directly drunk.