Adverse　weather　conditions　such　as　rain,　snow　and　fog　have　significant　impacts　on　highway　traffic　operation　and　safety.　This　paper　emphasized　rain　effects　on　characteristics　of　vehicle　speed,　based　on　the　traffic　and　road　weather　data　of　detectors　positioned　on　the　segment　between　Jinshan　and　Wuhannan　interchange　of　Jinggangao　(G4)　expressway　in　Hubei　province.　Focusing　on　the　rain　weather　element,　this　paper　analyzed　the　effects　of　rain　on　the　mean　speed　and　speed　variation　by　rain　or　non-rain　weather　or　under　different　rain　intensities;　speed　characteristics　were　deeply　explored　considering　different　factors　of　traffic　lane,　vehicle　types　and　time　hour,　utilizing　detailed　traffic　data　containing　traffic　lane　and　vehicle　type　information.　The　comprehensive　speed　prediction　model　under　rain　weather　condition　considering　several　factors　was　also　built　based　on　the　classic　traffic　flow　theory　of　V-K　relation　by　Greenshield,　and　the　goodness-of-fit　of　the　speed　prediction　model　reaches　80%　approximately.　The　research　results　can　be　useful　or　as　a　reference　to　the　analysis　of　rain　on　traffic　safety　and　operation,　traffic　capacity　analysis　under　or　decision-making　of　traffic　control　measures　such　as　variable　speed　limit　under　adverse　road　weather　conditions.　©,　2015,　Beijing　University　of　Technology.　All　right　reserved.