An ultrasonic sensor, which is installed on a test device, includes a shell, one end is open, the other end is closed surface; a cover sheet, bonded to the open end of the shell; a copper foil, a lower surface of the copper foil is bonded to an inner bottom surface of the closed surface of the shell; a piezoelectric chip, a lower surface of the piezoelectric chip is bonded to a upper surface of the copper foil, and when the test device vibrates, the piezoelectric chip converts a vibration signal into a voltage response signal; a cable, a positive electrode is welded on a upper surface of the piezoelectric chip, and a negative electrode is welded on the upper surface of the copper foil, configured to connect to an external detection device and transmit the voltage response signal to the external detection device.