Early acoustic wave monitoring method and system for gas cut in riser

The invention provides an early acoustic wave monitoring method and system for gas cut in a riser. The early acoustic wave monitoring system for gas cut in the riser comprises a riser system and an acoustic wave measuring system, wherein the riser system is arranged in seawater, and media of the riser system from inside to outside are sequentially a water hole, a drill string, a riser mixed fluid and a riser; the acoustic wave measuring system is composed of at least one transmitting transducer and a plurality of receiving transducers sleeved outside the riser, the transmitting transducer is used for exciting acoustic fields in the inner and outer spaces of the risers to produce acoustic wave inside a riser body material, and the receiving transducers are used for receiving the acoustic wave and judging the change of gas content of the mixed fluid in the riser according to the received acoustic wave.