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The performance and interference criteria for DC harmonics from high voltage direct current (HVDC) transmission lines are quite different from each other to each HVDC project up to now. With the developments of telecommunication circuits with giant anti-interference ability, such as light fiber and digital communication equipments and ultra-high voltage direct current (UHVDC) project in China, it is essential to map out practical and reasonable DC harmonics interference criteria for HVDC and UHVDC transmission lines based on the current conditions of telephone communication circuits. Taking into account the rigorous 4.5mV as the eventual telephone interference criteria for the DC transmission lines and a number of factors, for example, physical separation, shielding of telephone wires, circuit balance and ground resistivity, etc., the limitation of equivalent disturbing current as universal DC harmonics performance is calculated based on Xiangjiaba -Shanghai UHVDC (plusmn800 kV 6400 MW). According to the calculation results the reasonable DC harmonics interference criteria expressed by equivalent disturbing current for UHVDC transmission lines are presented and some effects from above factors on the interference criteria are discussed.