Though　flexible　electrochromic　devices　have　shown　huge　potential　application　in　the　fields　of　safety　warning,　display　and　smart　windows,　limited　attention　was　paid　on　preparing　flexible　electrochromic　fiber　because　of　the　difficulty　in　fabricating　the　multilayer　electrochromic　device　structure　in　one-dimensional　form.　In　this　study,　a　flexible　electrochromic　nylon　fiber　based　on　Ag　nanowires　(NWs)/PEDOT:PSS/WO3　nanoparticles　(NPs)　(PEDOT:PSS　=　poly(3,4-ethylenedioxythiophene):polystyrenesulfonic　acid)　is　successfully　fabricated,　delivering　rapid　color　switching　(2.5　and　9　s　for　bleaching　and　coloration)　and　high　optical　modulation　(65.5%　at　633　nm),　and　sustainable　to　repeated　mechanical　deformations.　Ag　NWs,　PEDOT:PSS　and　WO3　NPs　were　dip-coated　on　the　nylon　fiber,　resulting　in　an　electrochromic　fiber　electrode　with　stable　fiber　resistance　of　50–100　Ω/10　cm,　which　can　withstand　mechanical　deformation　against　300　times　of　bending　cycles　with　bending　radius　of　0.5　cm,　and　sustain　30　times　of　tape-peeling.　During　the　galvanostatic　tests,　the　capacitance　of　the　electrochromic　electrode　can　maintain　70%　of　the　initial　value　even　after　5,000　times　of　charge-discharge　cycles.　Even　in　knotted　shape,　the　fiber　still　shows　excellent　color　contrast.　This　study　provides　a　novel　method　to　construct　flexible　electrochromic　fiber　and　pave　the　way　for　the　development　of　flexible　optoelectronic　devices,　such　as　flexible　and　wearable　displays.　[Figure　not　available:　see　fulltext.].　©　2021,　Tsinghua　University　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.