Cow　dung　waste　has　caused　severe　environmental　pollution　and　public　health　issues　in　China.　In　this　study,　the　cow　dung　residues　were　used　as　a　cheap　renewable　fiber　to　modify　asphalt　binder,　providing　a　new　solution　for　the　proper　disposal　of　cow　dung　waste.　Three　cow　dung　fibers　with　two　lengths　were　prepared　using　different　treatments,　including　original　cow　dung　fiber　(CDF),　surface　treatments　of　cow　dung　fiber　(STCDF)　and　alkali　treatments　of　cow　dung　fiber　(ATCDF).　The　physicochemical　properties　of　CDF,　STCDF　and　ATCDF　were　analyzed　by　scanning　electron　microscope　(SEM)　and　thermogravimetry　(TG).　The　viscidity,　rheological　properties　and　fatigue　characteristics　of　CDF　modified　asphalt　binders　(CDFMA)　were　evaluated　using　Brookfield　viscometer　and　dynamic　shear　rheometer.　The　results　showed　that　the　rough　surfaces　of　STCDF　and　ATCDF　improved　their　thermal　stability.　STCDF　and　ATCDF　enhanced　the　resistance　to　permanent　deformation　under　high　temperature　conditions　of　modified　asphalt　binder.　STCDF　modified　asphalt　binders　exhibited　the　best　viscosity　and　rheological　performance.　The　increase　of　fiber　length　was　positively　correlated　with　the　high　temperature　deformation　resistance　of　CDFMA.　CDF,　STCDF　and　ATCDF　inhibited　fatigue　cracking　of　modified　asphalt　binders　compared　to　base　asphalt　binders.　ATCDF　modified　asphalt　binders　exhibited　higher　fatigue　life　and　smaller　crack　under　the　same　cyclic　loading.　The　increase　in　fiber　length　had　a　slight　improvement　on　the　fatigue　resistance　of　modified　asphalt　binders.