The invention discloses an ultrahigh-frequency sensor based on a high-voltage shunt reactor. Both ends of a metal housing of the ultrahigh-frequency sensor are respectively connected with a metal cover plate and an epoxy resin board, so that a closed cavity is formed, a shield plate divides the cavity into two closed spaces, a bracket is arranged on the inner wall of the metal housing of the lower space, an amplifier board is mounted on the bracket, an antenna board is mounted on the inner surface of the epoxy resin board, an aviation plug and N type connector is arranged on the wall of the metal housing of the upper space, and the antenna board, the amplifier board and the aviation plug and N type connector are sequentially connected in series through wires; and the lower end of the metal housing is fixedly connected with an annular plate. The ultrahigh-frequency sensor has a good effect of shielding outside electromagnetic signals, can ensure that the amplifier board and the antenna board in the housing can more accurately receive the electromagnetic waves generated by local discharge in the high-voltage shunt reactor, and is convenient to mount; and the ultrahigh-frequency sensor has strong anti-interference capability, great signal bandwidth, a wide dynamic range and high sensitivity.