Abstract: Oil-water two-phase pipe flow experiment has been conducted on horizontal multiphase flow experiment loop, made of stainless steel pipe with 26.1 inner-diameter and 30 m long, by using white oil and tap water as experimental medium. 7 different flow patterns have been found by detecting and watching flow pattern during the experiment process, which can fall into following 3 kinds: dispersed flow, stratified flow and semi-dispersed semi-stratified flow. Oil-water horizontal pipe flow pattern appearance and the transition between different flow patterns are depicted in detail. Also the oil-water pipe flow patterns are classified, according to their own different flow characteristic.