The acoustic emission(AE) technique was used to measure the AE signals of gas⁃liquid slug flow in horizontal pipes with non⁃intrusive and real⁃time monitoring features. Parameters of AE signals were calculated by setting window time and Critical Time of Elongated Bubble(CTEB). The characteristics of AE signal of slug unit were analyzed simultaneously. Based on the time delay of the same liquid slug arriving at two AE sensors, the AE method was used for detecting the translational velocity of liquid slug. Also, the measurement result of AE method was compared with the parallel conductivity method and Nicklin correlation. It is found that the AE signal of slug flow is very clear. The signals of liquid slug head, liquid slug body and elongated bubble decrease gradually and the signals of elongated bubble are below the threshold. The absolute energy and count of liquid slug increase with the superficial liquid and gas velocity respectively. AE technique could be used to monitor the frequency and translational velocity of liquid slug and it is a valuable method for application in the oil and gas field.