Abstract: In this paper, the research progress of slug flow in horizontal pipes at home and abroad is introduced in detail. The authors dissertate exhaustively the formation mechanism and characteristic parameters of slug flow in horizontal pipes, including slug lengths, void fraction, pressure drops and slug velocities. The imperfect fields about the research of slug flow in horizontal pipes at present are dissertated. The authors indicate the research emphases of slug flow in the future. The work aims at full and accurate expounding internal rules of slug flow in horizontal pipes. The authors expect that the work can conduce to experimental research and engineering application in slug flow.