To measure the EM environment parameters of a transmission line in bad weather conditions (such as rain, wind,etc) is difficult for technical staff. In the National Engineering Laboratory for UHV Technology (Kunming), a test line has been completed for EM enviroment tests. An automotive EM environment testing system was installed under the line, and the radio interference (RI), audible noise (AN), resultant electric field (Es) and ion current density (Js) at ground level were measured at all weather conditons with the voltage from ±800kV to ±1000kV over two years. Based on the measurement results, this paper has studied the influence of meteorological parameters on the EM enviroment of the transmisison line.