Seismic　fragility　analysis　is　a　common　tool　to　reveal　damage　progression　and　assess　structural　safety.　However,　the　existing　fragility　analysis　methodologies　for　sea-crossing　bridges　(SCBs)　cannot　effectively　balance　accuracy　and　computational　efficiency.　The　damage　characteristics　of　SCBs　under　the　multi-hazards　of　earthquake,　wind,　and　wave　remain　unclear.　In　this　paper,　a　novel　nonparametric　seismic　fragility　analysis　methodology,　named　NPCM,　was　developed.　This　technique　employs　log-transformed　Kernel　Density　Estimation　(log-TKDE)　to　model　the　marginal　cumulative　distributions　(MCDs)　of　structural　responses　and　the　intensity　measure　(IM)　of　ground　motions.　Thereafter,　it　establishes　the　joint　probability　distribution　(JPD)　and　solves　the　structural　fragility　curves　using　the　nonparametric　copula.　Taking　a　5-span　sea-crossing　cable-stayed　bridge　(SCCSB)　as　a　case　study,　the　reliability　and　accuracy　of　the　NPCM　were　comprehensively　confirmed　from　various　perspectives.　Factoring　in　the　stochastic　nature　of　disasters　and　the　interconnectedness　of　wind　and　waves　in　the　ocean　environment,　the　fragility　analysis　of　the　SCCSB　was　investigated.　The　structural　damage　behavior　and　anti-disaster　performance　subjected　to　earthquake　and　extreme　correlated　wind-wave　excitations　were　discussed.　The　results　demonstrate　that　log-TKDE　is　effective　in　obtaining　more　accurate　MCDs　than　the　Generalized　Pareto　Distribution　(GPD)　and　the　Generalized　Extreme　Value　(GEV)　distribution.　The　nonparametric　copula　can　provide　a　more　authentic　portrayal　of　the　intricate　interdependences　between　IM　and　the　responses　of　the　SCCSB　and　is　more　suitable　for　their　bivariate　JPD　modeling　than　parametric　copulas.　For　the　same　Bootstrap　sample　database,　NPCM　exhibits　a　narrower　confidence　interval　and　a　smoother　curve　than　Monte　Carlo　simulation　(MCS),　indicating　that　NPCM　has　satisfactory　credibility　and　superior　computational　efficiency.　Under　earthquake-wind-wave　excitations,　the　damage　probability　of　the　bearing　is　significantly　higher　than　that　of　the　tower　and　pier.　There　is　only　slight　damage　to　the　tower　and　moderate　damage　to　the　pier,　peaking　at　6.07%　and　1.00%,　respectively.　The　foundation　components　exhibit　gratifying　anti-disaster　qualities,　and　the　overall　structural　design　is　reliable.