The invention relates to the technical field of the electrical equipment, and especially relates to a mixed dielectric and medium-voltage or high-voltage electrical equipment. The invention disclosesa mixed dielectric, and comprises perfluoroolefine and hydrofluoroolefin; carbon atom number of each of the perfluoroolefine and hydrofluoroolefin is three; the global warming potential of the perfluoroolefine and hydrofluoroolefin is lower than that of the hydrofluoroolefin; the mole percent MFO of the perfluoroolefine and hydrofluoroolefin is not less than 95% of the mole percent M determined bythe formula M=(PFO/PMixture)*100, wherein the Pmixture is the pressure of the mixed dielectric in the electrical equipment at 20 DEG C, and the PFO is equal to the saturated vapor pressure at the lowest operation temperature of the perfluoroolefine and hydrofluoroolefin at the electrical equipment at 20 DEG C. The mixed dielectric is low in GWP value and high in saturated vapor pressure and dielectric constant, the defect that the dielectric insulation/arc-extinguishing performance is limited since the saturated vapor pressure of single perfluoroolefine or hydrofluoroolefin is not high enoughis overcome.