To　address　the　limitations　of　the　BWR　(Benedict-Webb-Rubin)　model　in　predicting　the　trend　of　the　real　gas　pressure　in　the　accumulator　under　the　medium　and　high　frequency　domain,　sinusoidal　excitation　experiments　with　different　frequencies　are　conducted　for　the　bladder　type　accumulator.　Based　on　the　delay　phenomenon　of　the　accumulator　found　in　the　experiment,　the　M-BWR　model　considering　the　delay　time　is　proposed.　To　verify　the　accuracy　of　the　model,　the　predicted　results　of　the　M-BWR　model　and　the　BWR　model　are　compared　with　the　experimental　results.　The　results　of　the　comparative　analysis　show　that　the　average　error　between　the　prediction　results　of　the　M-BWR　model　and　the　experimental　results　at　different　frequencies　is　less　than　8%,　which　meets　the　requirements　of　engineering　applications.　©　IMechE　2023.