Purpose:　Viscous　dampers　are　commonly　used　in　large　span　cable-stayed　bridges　to　mitigate　seismic　effects　and　have　achieved　great　success.　Design/methodology/approach:　However,　the　nonlinear　analysis　on　damper　parameters　is　usually　computational　intensive　and　nonobjective.　To　address　these　issues,　this　paper　proposes　a　simplified　method　to　determine　the　viscous　damper　parameters　for　double-tower　cable-stayed　bridges.　An　empirical　formula　of　the　equivalent　damping　ratio　of　viscous　dampers　is　established　through　decoupling　nonclassical　damping　structures　and　linearization　of　nonlinear　viscous　dampers.　Shaking　table　tests　are　conducted　to　verify　the　feasibility　of　the　proposed　method.　Moreover,　this　simplified　method　has　been　proved　in　long-span　cable-stayed　bridges.　Findings:　The　feasibility　of　this　method　is　verified　by　the　simplified　model　shaking　table　test.　This　simplified　method　for　determining　the　parameters　of　viscous　dampers　is　verified　in　cable-stayed　bridges　with　different　spans.　Originality/value:　This　simplified　method　has　been　validated　in　cable-stayed　bridges　with　various　spans.　©　2020,　Emerald　Publishing　Limited.