The utility model relates to an ultrasonic-based underground dust detecting device comprising a transducer, a CPLD (Complex Programmable Logic Device) unit, a signal conditioning circuit and a single chip microcomputer system; the transducer comprises an energy converter and an ultrasonic transmitting and receiving device; the energy converter is respectively connected with the CPLD unit and the transmitting end of the ultrasonic transmitting and receiving device; the receiving end of the ultrasonic transmitting and receiving device is located on the CPLD unit and connected with the signal conditioning circuit; the CPLD unit also comprises a comparing and measuring circuit; the comparing and measuring circuit comprises a phase comparator and a digital phase calculator; the comparing and measuring circuit is connected with the single chip microcomputer system; and the single chip microcomputer system comprises voice equipment and display equipment.