The invention discloses a calculation method of dielectric power factors of high-voltage electrical equipment. The method comprises that first direct current components of voltage and current signals are eliminated within the time domain, then fundamental frequency of electrical signals is accurately calculated according to the energy moment theory, then the primary signals are calculated in an interpolation mode according to a three-bending moment method, and complete alternation resampling is conducted, and last, the sample length of complete alternation is fast calculated in a Fourier mode to acquire phase included angles of fundamental wave voltage and fundamental wave current, tangents of other angles are acquired, and the dielectric power factors are acquired. The calculation method of the dielectric power factors of the high-voltage electrical equipment has the advantages of being not only capable of achieving accurate calculation of the dielectric power factors of the high-voltage electrical equipment, but also capable of accurately acquiring phase included angles between subharmonics of voltage and current signals, and detecting quality of electric energy by accurately measuring quality of the electric energy of the electrical signals.