The　submarine　cable　is　affected　by　the　complex　marine　environment　in　the　process　of　operation.　Once　the　fault　occurs,　it　will　cause　serious　economic　loss　and　social　impact.　Firstly,　this　paper　analyzes　and　classifies　the　causes　of　the　submarine　cable　fault.　Then,　according　to　the　history　data　of　faults,　the　static　reliability　model　based　on　the　length　of　submarine　cable　is　established,　which　reduces　the　calculation　error　for　the　long-term　reliability　evaluation　of　the　offshore　power　system.　Afterwards,　based　on　this　static　reliability　model,　an　improved　dynamic　reliability　model　with　time-varying　failure　rate　is　proposed,　which　provides　a　computational　basis　for　short-term　reliability　evaluation.　Finally,　the　practicability　and　accuracy　of　the　method　are　verified　by　an　example　of　submarine　cables　in　an　offshore　oilfield　power　grid.　©　2019　IEEE.