In order to improve the detection accuracy and reduce the detection time of harmonic signals in high-voltage distribution network, a harmonic signal detection method based on multi spectral line interpolation algorithm is proposed. Multi spectral line interpolation algorithm is used to extract the spectral features of harmonic signals. Based on the extracted spectrum characteristics of harmonic signal, the empirical mode decomposition of harmonic signal is carried out, and the ontology modal function is constructed to complete the detection of harmonic signal. The experimental results show that compared with the traditional harmonic signal detection methods, this method can accurately extract the spectral characteristics of harmonic signals in high-voltage power grid, so as to improve the detection accuracy of harmonic signals and reduce the detection time.