Abstract: A fiber bundle for bearing microorganisms. Fiber filaments are wound into a ring shape or have two ends bound into a bundle, or wires, ropes or bands made of staple fibers or fiber filaments are wound into a ring shape or have two ends bound into a bundle or are woven into a strip. A filter layer formed by fiber bundles for bearing microorganisms is characterized in large specific surface area and high porosity, and the unit capacity of bearing the microorganisms may be several times that of a granular filter material.