In order to investigate the effect of altitude on radio interference（RI） of AC power lines

a corona cage test system was used to measure the RI excitation function values of different bundle conductors in different altitude locations

such as Wuhan（23 m）

Jingyuan（1 408 m）

Xi’ning（2 261 m）

Gonghe（2 943 m）

and Yangbajin（4 300 m）.Then the influences of different altitudes

bundle numbers

and subconductor diameters on RI excitation function were obtained.A new altitude correction coefficient was proposed according to the fitting of measured data.The results show that

the actual RI altitude correction values fall in between the range of BPA correction calculation and Westinghouse correction calculation when the altitude below 3 200 m.Above 3 200 m

the measured correction values are less than the predicted values of both correction methods.The proposed RI correction term are applicable for different altitude RI correction when the altitude is less than 4 300 m.The conclusions presented in this paper can provide the technical support for the construction of AC transmission projects at high altitude area in China.