Abstract: The invention discloses an impedance spectrum in-situ measuring device for the dielectric constant of solid materials at high temperature and high pressure conditions. The device comprises a cube-shaped pyrophyllite, a cylindrical opening penetrates between one end face of the pyrophyllite and the other end face opposite to the end face; a heater formed by sleeving annular stainless steel sheets is arranged in the opening; a first plate-shaped platinum electrode and a second plate-shaped platinum electrode are arranged in the cavity of the innermost ring-shaped stainless steel sheet. The first plate-shaped platinum electrode is electrically connected with one end of the Solartron 1260 Impedance/Gainphase Analyzer through a first lead, and the second plate-shaped platinum electrode is electrically connected with the other end of the Solartron 1260 Impedance/Gainphase Analyzer through a second lead.