To ensure the construction of the new power system, the impact of power electronic equipment harmonics on main network is analysed. Three main characteristics of harmonics of the main network are analysed: massive distributed harmonic source access, amplification effect of line capacitance on harmonics and long-distance propagation of harmonics. The above factors overlap with each other, causing the current main network to generally exceed the standard. On the basis of following the recognized source control of "who pollutes, who treats", this paper explores the harmonic control of the main network, analyses the advantages and disadvantages of different control measures from the mechanism and case. The scheme of "who suffers, who treats" to implement terminal control is suggested at present and comprehensive harmonic control measures should be considered from the source, region power grid and the newly built main grid stations in the long run.