The invention discloses an ultrasonic wave partial discharge sensor designed with a high-precision signal frequency reduction circuit. The sensor comprises the high-precision signal frequency reduction circuit, and the high-precision signal frequency reduction circuit comprises a wave detection circuit and a wave filter circuit which are electrically connected with each other; the wave detection circuit comprises a first resistor R1, a second resistor R2, a third resistor R3, a first diode D1, a second diode D2, a first capacitor C1 and a second capacitor C2; the wave filter circuit comprisesa fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5 andan operational amplifier A. The ultrasonic wave partial discharge sensor designed with the high-precision signal frequency reduction circuit has the high-precision special signal frequency reductioncircuit, the structure of the circuit is simple, processing of small signals and large signals is integrated, and the detection precision and detection sensitivity of partial discharge can be greatlyimproved.