The　slug　flow　regime　may　be　appeared　in　subsea　gas-liquid　pipeline　of　the　offshore　petroleum　industry.　The　gas　entrainment　process　and　the　gas　bubble　distribution　in　liquid　slug　are　crucial　for　the　model　of　slug　flow.　An　experimental　facility　was　constructed　and　the　gas　bubble　distributions　in　the　liquid　slug　were　measured　by　the　dual-tip　conductivity　probe.　It　is　found　that　the　entrained　gas　is　broken　up　into　small　bubbles　by　the　high　turbulent　shear　stress　in　the　turbulent　shear　layer　in　the　mixing　zone.　The　small　bubbles　are　dispersed　completely　and　the　profiles　of　void　fraction　and　bubble　frequency　have　peaks　in　this　layer.　The　mechanism　of　gas　entrainment　is　also　presented.　©　(2011)　Trans　Tech　Publications,　Switzerland.