A one-transmitter and double-receiver downhole transducer is used for the single-hole acoustic wave test. The space between the transmitter and receiver 1 is 30cm while that between receiver 1 and receiver 2 is 20cm. Acoustic information is emitted and received along the wall in the borehole (the raw hole where well fluid is stored). During logging, the transducer is lowered to the bottom of the well or placed at the wellhead, and moved upward or downward according to the logging point distance. The wave train data collection and data storage are completed by the computer, and the longitudinal wave is picked up in the room through playback and data processing. In the waveform collected by the instrument, the initial arrival time of longitudinal wave is determined according to the jump point of the waveform, and the longitudinal wave velocity is calculated.