The invention discloses a dominant interharmonic spectrum distribution calculation method. The method comprises steps: a digital quantity for three-phase voltage and current signals of an M-frequencytime window is taken for discrete Fourier transform (DFT) analysis, and a rough interharmonic signal spectrum distribution diagram is acquired; according to the rough interharmonic signal spectrum distribution diagram, a harmonic singlet effective value and a harmonic cluster effective value are calculated, and the ratio of the harmonic cluster effective value to the harmonic singlet effective value is further calculated; according to the size relationship between the ratio and a threshold, whether interharmonics exist near the harmonics is judged; and if yes, the existence range of dominant interharmonics is determined, data in a certain time window are selected for DFT analysis, and the dominant interharmonic spectrum distribution is determined. Due to the method of the invention, the dominant interharmonic spectrum distribution can be simply and quickly; a help is provided for interharmonic control; influences on a power grid by the interharmonics are reduced; and safe and stable operation of power supply equipment and power consumption equipment.