Measuring the electromagnetic (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 was completed for EM environment tests. An automated EM environment testing system was installed under the line, the rad{o interference (RI), audible noise (AN), resultant electric field strength (E0), and ion current density (Js) at ground level were measured under all weather conditions within a voltage range from ±800 kV to ± 1 000 kV over two years. Based on the measurement results, the influence of meteorological parameters on the EM environment of the transmission line was studied. When the HR increases from 40 % to 80%, the RI, AN, E0, Js would have different degrees of attenuation. The RI on a rainy day is 3 dB lower than that of a sunny day, while the Js gets a sharp increase with the same weather condition change. In addition, AN and E0 are greatly influenced by wind speed: with increasing wind speed, E0 decreases and AN becomes unstable.