The　on-demand　modulation　of　defects　in　materials　for　the　effective　modulation　of　optical　nonlinearity　is　desirable,　while　it　remains　a　great　challenge.　In　this　work,　we　demonstrate　that　electrochemical　activation　is　a　facile　and　convenient　approach　to　modulating　the　broadband　third-order　nonlinear　absorption　of　nanoporous　tungsten　oxide　(WO3−x)　thin　film.　The　film　does　not　exhibit　optical　nonlinearity　at　the　initial　state,　while　shows　a　distinct　saturable　absorption　under　an　applied　voltage　of　−2.5　V　with　the　excitation　of　515,　800,　and　1,030　nm　laser.　The　nonlinear　absorption　coefficient　(βeff)　is　−766.38　±　6.67　cm·GW−1　for　1,030　nm　laser,　−624.24　±　17.15　cm·GW−1　for　800　nm　laser,　and　−120.70　±　11.49　cm·GW−1　for　515　nm　laser,　and　the　performance　is　competitive　among　inorganic　saturable　absorbers.　The　activation　is　accomplished　in　2　min.　The　performance　enhancement　is　ascribed　to　the　formation　of　abundant　in-gap　defect　states　because　of　the　reduction　of　the　tungsten　atoms,　and　a　Pauli-blocking　effect　occurs　during　the　excitation　of　in-gap　defect　states.　The　small　feature　size　of　WO3−x　(∼　12　nm)　enables　the　effective　and　fast　introduction　and　removal　of　the　defects　in　porous　film,　and　accordingly　the　fast　and　broadband　modulation　of　optical　nonlinearity.　Our　results　suggest　a　controllable,　effective,　and　convenient　approach　to　tuning　the　nonlinear　absorption　of　materials.　[Figure　not　available:　see　fulltext.]　©　2021,　Tsinghua　University　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.