Abstract: The power line harmonic radiation (PLHR) becomes a man-made pollution source to the near-Earth space. Both the research history and present status of PLHR were introduced. The research involves the observations of such phenomenon on the ground and onboard satellites, and the qualitative and quantitative analysis of its generation mechnism. Especially, the PLHR observed recently on DEMETER satellite were introduced. Based on the present research result, some unsolved problems were put forward. With the development of electrical industry and the launch of the testing satellite monitoring seismic electromagnetic signals in China, PLHR in upper space needs to pay close attention.