The invention which relates to a biologically slow filtering filler and a manufacturing method thereof belongs to the field of water treatment. The manufacturing method of the biologically slow filtering filler comprises the following steps: a, introducing a host material into a chitosan solution, and stirring, wherein the surface of the host material is treated by a plasticizer; b, adding a crosslinking agent and stirring; c, carrying out a crosslinking reaction; and d, drying. According to the biologically slow filtering filler obtained through the manufacturing method of the invention or the biologically slow filtering filler of the present invention, a problem of a chitosan crosslinking substance loss with water is alleviated, and the chitosan crosslinking substance can well performs effects.