Electromagnetic environments generated by power transmission system, possibilities of the interference and its mitigation method was introduced. In the frequency region below 10kHz, concern for DC and AC electric and magnetic field are described. In the frequency range above 10kHz, concern for discharges on power apparatus, electromagnetic emvironments generated by carrier system and fault locating system and passive interference are described. Electromagnetic environment caused by load equipments, that is harmonics, and undesirable electromagnetic emission from power converting units are described finally.