Due to the high voltage operation of transmission lines, corona discharge phenomena are quite common around AC and DC transmission lines. A large amount of positive and/or negative ions are generated during the corona processes. The effects of corona space charge arising from HVDC transmission lines are much more significant than that in AC transmission lines due to the extended distribution of the DC space charge. The space charge greatly influences the audible noise, radio interference, and the electric field strength on the ground and in space, which are very important environmental considerations for HVDC transmission lines. Therefore, line designers must predict the audio noise (AN), radio interference (RI) and the electric field strength around HVDC transmission lines. A convenient, powerful computer program called ?SESEnviroPlus? has been developed to fulfill the need for such calculations. Corona discharge is influenced by many factors, including those depending on line design such as the operating voltage and system configuration, and external factors such as ambient weather conditions, ground resistivity, altitude, etc. Then, the calculation of AN, RI and the space charge electric field strength produced by a transmission line due to occurrence of corona on conductors should be based on these parameters.