According to the radio interference equation of bipolar DC transmission lines drawn by international special committee on radio interference

the radio interference from UHVDC transmission lines based on polished rod with unequal height is discussed. The equivalent charge of conductor at average height is acquired by using image method

and the maximum field strength on conductor surface is calculated by regulation method. During the calculation of radio interference

the minimum height to ground is the result that the average height subtract one third of arc sag

which is the traditional calculation method. In order to have more accurate value

the minimum height to ground is redefined based on polished rod with unequal height

and the average height equation of conductor is deduced. Based on the ±800 kV DC transmission line of Xiangjiaba to Shanghai

the distribution of radio interference is discussed

and the result drawn by two calculation methods is compared. It is found that the span distance

the height difference

and the meteorological are needed to take into account during the radio interference calculation

especially the transmission line with long span distance and large height difference.