Traceability of harmonic sources in power system is the premise and foundation of harmonic assessment and management. Combining with the development of harmonics traceability at home and abroad, the physical and mathematical meanings of harmonic source traceability on three different levels are clearly pointed out from two aspects of PCC point harmonic current and harmonic voltage responsibility division, and the differences and similarities with Thevenin and Norton equivalent circuit models for harmonic source identification are analyzed in detail. From two levels of quality and quantity analysis, combining with the two different circuit models, this paper summarizes the key problems and difficulties in the implementation of the above-mentioned traceability methods. Based on the new development of current power grid technology, the research on harmonic traceability in the future is discussed.