In order to expand the thickness measurement range of the propellant gain of high-attenuation solid rocket motor, the theoryofstaticcomponent(SC) generated by ultrasoniclongitudinalwavein solidpropagation isused in this paper. Through the combination ofreflectiveultrasonictransducerswith onetransmitterand two receivers, theworking frequency of the ultrasonic transducer at the transmitter is 500 kHz, and the working frequency of the ultrasonic transducerat the receiving end is 50 and 500 kHz respectively, to complete the static measurement of a variety of thickness of propellant gain. The measurement results show that the 50 kHz ultrasonic transducer can amplify and receive the low-frequencySC signal excited by the 500 kHz ultrasonic longitudinal wave for the larger thickness of the propellantgain, and the500kHzcanreceivethe500kHzfundamentalsignaland thelow-frequencySC signalatthesame time forthe smallerthickness ofthe propellantgain. Compared with the traditionaltransducercombination ofthe same frequency transceiver, the transducer combination of one transmitter and two receivers improves the measurable thickness rangewithoutincreasingtheblind areaofthicknessmeasurement. And itcan completethemeasurementin the thickness range of20~ 200 mm , which has acertain degree ofinnovation and good practicalvalue.