Experimental　investigations　on　slug　flow　were　carried　out　in　horizontal　helical　rectangular　channel　by　using　high　speed　flow　visualization.　Evolution　of　slug　in　the　whole　helical　rectangular　channel　was　presented　and　the　fine　features　of　slug　flow　in　different　positions　were　illustrated.　The　slug　characteristics　changed　along　the　axial　direction　due　to　the　combined　effects　of　gravitational　and　centrifugal　force.　Based　on　the　experimental　data,　slug　velocity,　slug　frequency　and　length　distribution　in　different　positions　were　given.　The　present　topography　measurement　illustrated　the　evolution　features　of　liquid　film　thickness,　which　was　determined　by　the　effect　of　centrifugal　force　and　gravity.　Liquid　film　falling　velocity　decreased　as　the　slug　moved　upward　and　was　visibly　increasing　in　the　downward　flow.　©All　Rights　Reserved.