The　characteristics　of　severe　slugging　flow　was　investigated　experimentally　in　a　long　pipeline-riser　under　the　pressure　of　1　MPa.　Based　on　the　power　spectral　density　(PSD)　function　of　the　pressure　difference　signal　of　the　riser,　the　variation　of　the　severe　slugging　frequency　with　the　air-water　flow　rate　and　top-choking　was　analysed.　The　experimental　results　show　that　the　frequency　of　severe　slugging　flow　increases　with　the　increase　of　gas　and　liquid　flow　rate,　but　the　increased　amplitude　is　greater　for　liquid.　In　the　process　of　throttling　severe　slugging　flow　to　steady-state,　the　frequency　of　severe　slugging　is　increased　when　throttling　at　the　area　of　SS1　where　the　flow　rate　is　extremely　low,　while　almost　unchanged　in　the　area　of　SS1　and　SS2　where　a　larger　gas　and　liquid　flow　rate.　©　2022,　Science　Press.　All　right　reserved.