The invention discloses an antibacterial polyurethane fiber and a preparation method thereof. On a dry weight basis, the prepared antibacterial polyurethane fiber contains 0.01%-1.0% of nano-silver in weight percentage. The size and shape of the nano-silver are controllable, and the nano-silver can be uniformly distributed at the interior and on the surface of the fiber. The antibacterial polyurethane fiber has the advantages that an antimicrobial spectrum is wide, the antibiosis is long-lasting, toxic and side effects are few, the preparation method is simple, the spinnability and post-fabricability are good, and the like, thus being widely applied to the fields of medical materials, spinning materials and the like.