The utility model discloses a device for accurately measuring an ultrasonic attenuation coefficient. The device comprises a support, a signal generator and an oscilloscope and is characterized in that two ends of the support are provided with an ultrasonic energy transducer I and an ultrasonic energy transducer II, wherein the ultrasonic energy transducer I and the ultrasonic energy transducer II are the same, and the ultrasonic energy transducer II can freely move along the support; the support is provided with a stopper; outer sides of the support, the ultrasonic energy transducer I and the ultrasonic energy transducer II are provided with an synthetic glass case; the ultrasonic energy transducer I is connected with the signal generator, and the ultrasonic energy transducer II are connected with the oscilloscope. The device is additionally provided with a sound-absorbing cotton layer and the stopper without changing the structure of a commonly used instrument, eliminates measurement errors caused b reflection waves and the shapes and dimensions of the ultrasonic energy transducers, raises measurement accuracy, is low in cost, and is more accurate in measurement result compared with an original result.