The invention relates to a device for ultrasonically measuring the thickness of a gas-liquid two-phase flow circumferential liquid film. The device comprises an ultrasonic transducer, a measuring pipeline and flanges fixed at the two ends of the measuring pipeline; a plurality of openings are formed in the outer wall of the measuring pipeline in the circumferential direction; a fixing sleeve is arranged; a plurality of through holes penetrating through the fixing sleeve are also formed in the circumferential direction of the fixing sleeve, corresponding to the peripheral direction of the outerwall of the measuring pipeline; the through holes in the fixing sleeve are connected on one side of the fixing sleeve, and are used for leading out ultrasonic transducer cable line ports; the fixingsleeve is fixedly connected with the measuring pipeline; the openings of the measuring pipeline are aligned with the through holes of the fixing sleeve one by one respectively; the through holes of the fixing sleeve can contain the ultrasonic transducer and are provided with internal threads; the ultrasonic transducer is fixed in the through holes through compression screws; the flanges adopt widened flanges; and the flanges at the two ends are fixedly connected through tensioning lead screws.